Shaped glass laminates and methods for forming the same

ABSTRACT

Embodiments of a laminate including a first curved glass substrate comprising a first viscosity (poises) at a temperature of 630° C.; a second curved glass substrate comprising a second viscosity that is greater than the first viscosity at a temperature of 630° C.; and an interlayer disposed between the first curved glass substrate and the second curved glass substrate, are disclosed. In one or more embodiments, the first curved glass substrate exhibits a first sag depth that is within 10% of a second sag depth of the second curved glass substrate. In one or more embodiments, the first glass substrate and the second glass substrate exhibit a shape deviation therebetween of about ±5 mm or less as measured by an optical three-dimensional scanner or exhibit minimal optical distortion. Embodiments of vehicles including such laminates and methods for making such laminates are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/899,689 filed on Feb. 20, 2018 which claims the benefit of priorityunder 35 U.S.C. § 119 of U.S. Provisional Application Ser. No.62/586,938 filed on Nov. 16, 2017, U.S. Provisional Application Ser. No.62/461,494 filed on Feb. 21, 2017, and U.S. Provisional Application Ser.No. 62/461,080 filed on Feb. 20, 2017, the content of which is reliedupon and incorporated herein by reference in its entirety.

BACKGROUND

The disclosure relates to shaped glass laminates and methods for formingsuch laminates, and more particularly to shaped glass laminatesincluding glass substrates that differ from one another and exhibit withminimal shape mismatch between one another.

A typical glass laminate is shown in FIG. 1 and includes a first curvedglass substrate 110, a second curved glass substrate 120, and anintervening interlayer 130 disposed between the first curved glasssubstrate and the second curved glass substrate. Such laminates aretypically formed by shaping or curving a first glass substrate and asecond glass substrate simultaneously to provide a first curved glasssubstrate and a second glass substrate having a substantially similar oridentical shape to one another. Various methods are used to shape theglass substrates including co-shaping which shape both glass substratessimultaneously by stacking by the glass substrates on top of one anotherto form a stack and co-shaping the stack. Methods of co-shaping includeco-sagging which uses gravity to sag or shape a pair or stack of thefirst and second glass substrates simultaneously while heating the stackuntil the stack reaches a viscoelastic phase. Other methods includeco-shaping using molds or a vacuum alone or in combination with oneanother or in combination with co-sagging.

One co-shaping example is illustrated in FIG. 2, which shows a bendingframe 200 that has a first radius of curvature R1, and a second radiusof curvature R2 to form a complexly curved glass substrate byco-sagging. To co-sag two glass substrates, such glass substrates arestacked on top of one another with intervening separation powder, whichmay include calcium carbonate. The stack is placed on the bending frameand the stack and bending frame are heated in a furnace until the glasssubstrates achieve a temperature equal to their softening temperature.At such a temperature, the glass substrates are bent or sagged bygravity. In some embodiments, a vacuum and/or mold can be used tofacilitate co-sagging.

In such known laminates, the glass substrates have a thickness in arange from about 1.6 mm to about 3 mm. In some known laminates, thefirst glass substrate and the second glass substrate have respectivecompositions that are substantially identical or substantially similarto one another and thus properties similar to one another.

There is a need for laminates that are lightweight and thus thinner toreduce the weight of vehicles that incorporate such laminates.Accordingly, there is a need for laminates with thinner glass substratesand potentially laminates with two compositionally different glasssubstrates.

SUMMARY

A first aspect of this disclosure pertains to a laminate including afirst curved glass substrate comprising a first major surface, a secondmajor surface opposing the first major surface, a first thicknessdefined as the distance between the first major surface and second majorsurface, and a first sag depth of about 2 mm or greater, the firstcurved glass substrate comprising a first viscosity (poises) at atemperature of 630° C.; a second curved glass substrate comprising athird major surface, a fourth major surface opposing the third majorsurface, a second thickness defined as the distance between the thirdmajor surface and the fourth major surface, and a second sag depth ofabout 2 mm or greater, the second curved glass substrate comprising asecond viscosity that is greater than the first viscosity at atemperature in a range from about 590° C. to about 650° C. (or at about630° C.); and an interlayer disposed between the first curved glasssubstrate and the second curved strengthened glass substrate andadjacent the second major surface and third major surface. In one ormore embodiments, the first sag depth is within 10% of the second sagdepth and a shape deviation between the first glass substrate and thesecond glass substrate of ±5 mm or less as measured by an opticalthree-dimensional scanner, and wherein one of or both the first majorsurface and the fourth major surface exhibit an optical distortion ofless than 200 millidiopters as measured by an optical distortiondetector using transmission optics according to ASTM 1561, and whereinthe first major surface or the second major surface comprises a membranetensile stress of less than 7 MPa as measured by a surface stressmeter,according to ASTM C1279.

A second aspect of this disclosure pertains to a vehicle comprising: abody defining an interior and an opening in communication with theinterior; laminate according to one or more embodiments disposed in theopening, wherein the laminate is complexly curved.

A third aspect of this disclosure pertains to a method for forming acurved laminate comprising: forming a stack comprising a first glasssubstrate comprising a first viscosity (poises) and a first sagtemperature and a second glass substrate, the second glass substratecomprising a second viscosity that greater than the first viscosity at atemperature of 630° C.; and heating the stack and co-shaping the stackto form a co-shaped stack, the co-shaped stack comprising a first curvedglass substrate having a first sag depth and a second curved glasssubstrate each having a second sag depth, wherein the first sag depthand the second sag depth are greater than 2 mm and within 10% of oneanother. In some embodiments, the second sag temperature that differsfrom the first sag temperature by about 5° C. or greater, about 10° C.or greater, about 15° C. or greater, about 20° C. or greater, about 25°C. or greater, about 30° C. or greater, or about 35° C. or greater.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments as described herein, including the detailed descriptionwhich follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understanding the natureand character of the claims. The accompanying drawings are included toprovide a further understanding, and are incorporated in and constitutea part of this specification. The drawings illustrate one or moreembodiment(s), and together with the description serve to explainprinciples and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side-view of a known glass laminate;

FIG. 2 is a perspective view of a known bending frame used to shapeglass substrates and laminates

FIG. 3 is a side view of shaped laminate according to one or moreembodiments;

FIG. 3A is a side view of a shaped laminate according to one or moreembodiments;

FIG. 4 is a graph showing the viscosity of three different glasssubstrates as a function of temperature;

FIG. 5 is a side view of a glass substrates according to one or moreembodiments;

FIG. 6 is a side view of a glass substrates according to one or moreembodiments;

FIG. 7 is a perspective view of a vehicle according to one or moreembodiments;

FIG. 8 is a side cross-sectional view of a lehr furnace that can be usedin a method according to one or more embodiments of a method for forminga curved laminate;

FIG. 9 is an illustration of a co-shaping simulation of two glasssubstrates, with air flow effects.

FIG. 10 plots the temperature profile as a function of time used for thesimulation shown in FIG. 9.

FIG. 11 illustrates the changes in pressure magnitude across the area ofthe glass substrate stack without a temporary bond between the glasssubstrates from near the center point to a corner of the stack;

FIG. 12 is an illustration of a simulation of reinforcement that formsand/or maintains a temporary bond between the glass substrates duringco-shaping;

FIG. 13 illustrates the changes in pressure magnitude across the area ofthe glass substrate stack with a temporary bond between the glasssubstrates from near the center point to a corner of the stack;

FIGS. 14A-B illustrate shape measurements of Example E;

FIGS. 15A-B illustrate shape measurements of Example F;

FIGS. 16A-C illustrate shape measurements of Example G; and

FIGS. 17A-C illustrate shape measurements of Example H.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments, examples ofwhich are illustrated in the accompanying drawings.

Aspects of this disclosure pertain to glass laminates that are thin orhave a reduced weight compared to conventional laminates, whileexhibiting superior strength and meeting regulatory requirements for usein automotive and architectural applications. Conventional laminatesinclude two soda lime silicate glass substrates having a thickness in arange from about 1.6 mm to about 3 mm. To reduce the thickness of atleast one of the glass substrates, while maintaining or improving thestrength and other performance of the laminate, one of the glasssubstrates can include a strengthened glass substrate which tends tohave very different viscosity as a function of temperature (or viscositycurve) than the soda lime silicate glass substrate. In particular,typical strengthened glass substrates exhibit a significantly higherviscosity at a given temperature than soda lime silicate glasssubstrates.

It was previously believed that co-shaping, and in particularco-sagging, such differing glass substrates, was not possible due to thedifference in viscosity curves. However, as will be described herein,such successful co-shaping (including co-sagging) can be achieved toform a laminate that exhibits substantially minimal shape mismatch,minimal stress due to co-shaping, and low or substantially low opticaldistortion.

It was also generally understood that a glass substrate with lowerviscosity (e.g., soda lime silicate glass substrate) could be co-saggedwith a higher viscosity glass substrate by positing the lower viscosityglass substrate on top of the higher viscosity glass substrate. Inparticular, it was believed that the opposite configuration, the lowerviscosity glass substrate would sag to a deeper depth than the higherviscosity glass substrate. Surprisingly, as will be described herein,successful co-sagging can be achieved with this oppositeconfiguration—that is, the higher viscosity glass substrate is placed ontop of the lower viscosity glass substrate. Such co-sagged glasssubstrates exhibit substantially identical shapes, while achieving adeep or large sag depth, and can be laminated together with aninterlayer between the glass substrates to form a shaped laminateexhibiting minimal optical and stress defects.

As used herein, the phrase “sag depth” refers to the maximum distancebetween two points on the same convex surface of a curved glasssubstrate, as illustrated in FIG. 3 by reference characters “318” and“328”. As illustrated in FIG. 3, the point on the convex surface at theedge and the point on the convex surface at or near the center of theconvex surface provide the maximum distance 318 and 328.

A first aspect of this disclosure pertains to a laminate 300 comprisinga first curved glass substrate 310, a second curved glass substrate 320and an interlayer 330 disposed between the first curved glass substrateand the second curved glass substrate, as illustrated in FIG. 3. In oneor more embodiments, the first curved glass substrate 310 includes afirst major surface 312, a second major surface 314 opposing the firstmajor surface, a minor surface 313 extending between the first majorsurface and the second major surface, a first thickness 316 defined asthe distance between the first major surface and second major surface,and a first sag depth 318. In one or more embodiments, the first curvedglass substrate 310 includes a peripheral portion 315 that extends fromthe minor surface 313 toward the internal portion of the first glasssubstrate. In one or more embodiments, the second curved glass substrate320 includes a third major surface 322, a fourth major surface 324opposing the third major surface, a minor surface 323 extending betweenthe first major surface and the second major surface, a second thickness326 defined as the distance between the third major surface and thefourth major surface, and a second sag depth 328. In one or moreembodiments, the first curved glass substrate 310 includes a peripheralportion 325 that extends from the minor surface 323 toward the internalportion of the first glass substrate.

The first glass substrate 310 has a width defined as a first dimensionof one of the first and second major surfaces that is orthogonal to thethickness, and a length defined as a second dimension of one of thefirst and second major surfaces orthogonal to both the thickness and thewidth. The first glass substrate 320 has a width defined as a firstdimension of one of the first and second major surfaces that isorthogonal to the thickness, and a length defined as a second dimensionof one of the first and second major surfaces orthogonal to both thethickness and the width. In one or more embodiments, the peripheralportion 315, 325 of one of or both the first and second glass substratesmay have a peripheral length extending from the minor surface 313, 323that is less than about 20% of the respective length and widthdimensions of the first and second glass substrates. In one or moreembodiments, the peripheral portion 315, 325 may have a peripherallength extending from the minor surface 313, 323 that is about 18% orless, about 16% or less, about 15% or less, about 14% or less, about 12%or less, about 10% or less, about 8% or less, or about 5% or less of therespective length and width dimensions of the first and second glasssubstrates.

In one or more embodiments, the interlayer 330 is disposed between thefirst curved glass substrate and the second curved glass substrate suchthat it is adjacent the second major surface 314 and third major surface322, as shown in FIG. 3.

In the embodiment shown in FIG. 3, the first surface 312 forms a convexsurface and the fourth surface 324 forms a concave surface. In theembodiment of the laminate 300A shown in FIG. 3A, the position of theglass substrates may be interchanged such that the interlayer 330 isdisposed between the first curved glass substrate 310 and the secondcurved glass substrate 320 such that it is adjacent the first majorsurface 312 and fourth major surface 324. In such embodiments, thesecond surface 314 forms a convex surface and the third surface 322forms a concave surface, as shown in FIG. 3A.

In one or more embodiments, the first curved glass substrate (or thefirst glass substrate used to form the first curved glass substrate)exhibits a first viscosity (in units of poise) and the second curvedglass substrate (or the second glass substrate used to form the secondcurved glass substrate) exhibits a second viscosity (in units of poise)that differs from the first viscosity at a given temperature. The giventemperature in some embodiments may be from about 590° C. to about 650°C. (or at about 630° C.). In some embodiments, the second viscosity isequal to or greater than about 2 times, about 3 times, about 4 times,about 5 times, about 6 times, about 7 times, about 8 times, about 9times, or about 10 times the first viscosity, at a temperature of 630°C. In one or more embodiments, the second viscosity may be greater thanor equal to 10 times the first viscosity at a given temperature. In oneor more embodiments, the second viscosity is in a range from about 10times the first viscosity to about 1000 times the first viscosity (e.g.,from about 25 times to about 1000 times the first viscosity, from about50 times to about 1000 times, from about 100 times to about 1000 times,from about 150 times to about 1000 times, from about 200 times to about1000 times, from about 250 times to about 1000 times, from about 300times to about 1000 times, from about 350 times to about 1000 times,from about 400 times to about 1000 times, from about 450 times to about1000 times, from about 500 times to about 1000 times, from about 10times to about 950 times, from about 10 times to about 900 times, fromabout 10 times to about 850 times, from about 10 times to about 800times, from about 10 times to about 750 times, from about 10 times toabout 700 times, from about 10 times to about 650 times, from about 10times to about 600 times, from about 10 times to about 550 times, fromabout 10 times to about 500 times, from about 10 times to about 450times, from about 10 times to about 400 times, from about 10 times toabout 350 times, from about 10 times to about 300 times, from about 10times to about 250 times, from about 10 times to about 200 times, fromabout 10 times to about 150 times, from about 10 times to about 100times, from about 10 times to about 50 times, or from about 10 times toabout 25 times the first viscosity.

In one or more embodiments in which the first glass substrate and/or thesecond glass substrate (or the first glass substrate and/or second glasssubstrate used to form the first curved glass substrate and secondcurved glass substrate, respectively) includes a mechanicallystrengthened glass substrate (as described herein), the first and/orsecond viscosity may be a composite viscosity.

In one or more embodiments, at 600° C., the first viscosity is in arange from about 3×10¹⁰ poises to about 8×10¹⁰ poises, from about 4×10¹⁰poises to about 8×10¹⁰ poises, from about 5×10¹⁰ poises to about 8×10¹⁰poises, from about 6×10¹⁰ poises to about 8×10¹⁰ poises, from about3×10¹⁰ poises to about 7×10¹⁰ poises, from about 3×10¹⁰ poises to about6×10¹⁰ poises, from about 3×10¹⁰ poises to about 5×10¹⁰ poises, or fromabout 4×10¹⁰ poises to about 6×10¹⁰ poises.

In one or more embodiments, at 630° C., the first viscosity is in arange from about 1×10⁹ poises to about 1×10¹⁰ poises, from about 2×10⁹poises to about 1×10¹⁰ poises, from about 3×10⁹ poises to about 1×10¹⁰poises, from about 4×10⁹ poises to about 1×10¹⁰ poises, from about 5×10⁹poises to about 1×10¹⁰ poises, from about 6×10⁹ poises to about 1×10¹⁰poises, from about 1×10⁹ poises to about 9×10⁹ poises, from about 1×10⁹poises to about 8×10⁹ poises, from about 1×10⁹ poises to about 7×10⁹poises, from about 1×10⁹ poises to about 6×10⁹ poises, from about 4×10⁹poises to about 8×10⁹ poises, or from about 5×10⁹ poises to about 7×10⁹poises.

In one or more embodiments, at 650° C., the first viscosity is in arange from about 5×10⁸ poises to about 5×10⁹ poises, from about 6×10⁸poises to about 5×10⁹ poises, from about 7×10⁸ poises to about 5×10⁹poises, from about 8×10⁸ poises to about 5×10⁹ poises, from about 9×10⁸poises to about 5×10⁹ poises, from about 1×10⁹ poises to about 5×10⁹poises, from about 1×10⁹ poises to about 4×10⁹ poises, from about 1×10⁹poises to about 3×10⁹ poises, from about 5×10⁸ poises to about 4×10⁹poises, from about 5×10⁸ poises to about 3×10⁹ poises, from about 5×10⁸poises to about 2×10⁹ poises, from about 5×10⁸ poises to about 1×10⁹poises, from about 5×10⁸ poises to about 9×10⁸ poises, from about 5×10⁸poises to about 8×10⁸ poises, or from about 5×10⁸ poises to about 7×10⁸poises.

In one or more embodiments, at 600° C., the second viscosity is in arange from about 2×10¹¹ poises to about 1×10¹⁵ poises, from about 4×10¹¹poises to about 1×10¹⁵ poises, from about 5×10¹¹ poises to about 1×10¹⁵poises, from about 6×10¹¹ poises to about 1×10¹⁵ poises, from about8×10¹¹ poises to about 1×10¹⁵ poises, from about 1×10¹² poises to about1×10¹⁵ poises, from about 2×10¹² poises to about 1×10¹⁵ poises, fromabout 4×10¹² poises to about 1×10¹⁵ poises, from about 5×10¹² poises toabout 1×10¹⁵ poises, from about 6×10¹² poises to about 1×10¹⁵ poises,from about 8×10¹² poises to about 1×10¹⁵ poises, from about 1×10¹³poises to about 1×10¹⁵ poises, from about 2×10¹³ poises to about 1×10¹⁵poises, from about 4×10¹³ poises to about 1×10¹⁵ poises, from about5×10¹³ poises to about 1×10¹⁵ poises, from about 6×10¹³ poises to about1×10¹⁵ poises, from about 8×10¹³ poises to about 1×10¹⁵ poises, fromabout 1×10¹⁴ poises to about 1×10¹⁵ poises, from about 2×10¹¹ poises toabout 8×10¹⁴ poises, from about 2×10¹¹ poises to about 6×10¹⁴ poises,from about 2×10¹¹ poises to about 5×10¹⁴ poises, from about 2×10¹¹poises to about 4×10¹⁴ poises, from about 2×10¹¹ poises to about 2×10¹⁴poises, from about 2×10¹¹ poises to about 1×10¹⁴ poises, from about2×10¹¹ poises to about 8×10¹³ poises, from about 2×10¹¹ poises to about6×10¹³ poises, from about 2×10¹¹ poises to about 5×10¹³ poises, fromabout 2×10¹¹ poises to about 4×10¹³ poises, from about 2×10¹¹ poises toabout 2×10¹³ poises, from about 2×10¹¹ poises to about 1×10¹³ poises,from about 2×10¹¹ poises to about 8×10¹² poises, from about 2×10¹¹poises to about 6×10¹² poises, or from about 2×10¹¹ poises to about5×10¹² poises.

In one or more embodiments, at 630° C., the second viscosity is in arange from about 2×10¹⁰ poises to about 1×10¹³ poises, from about 4×10¹⁰poises to about 1×10¹³ poises, from about 5×10¹⁰ poises to about 1×10¹³poises, from about 6×10¹⁰ poises to about 1×10¹³ poises, from about8×10¹⁰ poises to about 1×10¹³ poises, from about 1×10¹¹ poises to about1×10¹³ poises, from about 2×10¹¹ poises to about 1×10¹³ poises, fromabout 4×10¹¹ poises to about 1×10¹³ poises, from about 5×10¹¹ poises toabout 1×10¹³ poises, from about 6×10¹¹ poises to about 1×10¹³ poises,from about 8×10¹¹ poises to about 1×10¹³ poises, from about 1×10¹²poises to about 1×10¹³ poises, from about 2×10¹⁰ poises to about 8×10¹²poises, from about 2×10¹⁰ poises to about 6×10¹² poises, from about2×10¹⁰ poises to about 5×10¹² poises, from about 2×10¹⁰ poises to about4×10¹² poises, from about 2×10¹⁰ poises to about 2×10¹² poises, fromabout 2×10¹⁰ poises to about 1×10¹² poises, from about 2×10¹⁰ poises toabout 8×10¹¹ poises, from about 2×10¹⁰ poises to about 6×10¹¹ poises,from about 2×10¹⁰ poises to about 5×10¹¹ poises, from about 2×10¹⁰poises to about 4×10¹¹ poises, or from about 2×10¹⁰ poises to about2×10¹¹ poises.

In one or more embodiments, at 650° C., the second viscosity is in arange from about 1×10¹⁰ poises to about 1×10¹³ poises, from about 2×10¹⁰poises to about 1×10¹³ poises, from about 4×10¹⁰ poises to about 1×10¹³poises, from about 5×10¹⁰ poises to about 1×10¹³ poises, from about6×10¹⁰ poises to about 1×10¹³ poises, from about 8×10¹⁰ poises to about1×10¹³ poises, from about 1×10¹¹ poises to about 1×10¹³ poises, fromabout 2×10¹¹ poises to about 1×10¹³ poises, from about 4×10¹¹ poises toabout 1×10¹³ poises, from about 4×10¹¹ poises to about 1×10¹³ poises,from about 5×10¹¹ poises to about 1×10¹³ poises, from about 6×10¹¹poises to about 1×10¹³ poises, from about 8×10¹¹ poises to about 1×10¹³poises, from about 1×10¹² poises to about 1×10¹³ poises, from about1×10¹⁰ poises to about 8×10¹² poises, from about 1×10¹⁰ poises to about6×10¹² poises, from about 1×10¹⁰ poises to about 5×10¹² poises, fromabout 1×10¹⁰ poises to about 4×10¹² poises, from about 1×10¹⁰ poises toabout 2×10¹² poises, from about 1×10¹⁰ poises to about 1×10¹² poises,from about 1×10¹⁰ poises to about 8×10¹¹ poises, from about 1×10¹⁰poises to about 6×10¹¹ poises, from about 1×10¹⁰ poises to about 5×10¹¹poises, from about 1×10¹⁰ poises to about 4×10¹¹ poises, from about1×10¹⁰ poises to about 2×10¹¹ poises, or from about 1×10¹⁰ poises toabout 1×10¹¹ poises.

An example of viscosity as a function of temperature of an exemplaryfirst curved glass substrate (designated A) and two exemplary secondcurved glass substrates (designated B1 and B2) are shown in FIG. 4.

In one or more embodiments, the combination of the first glass substrateand the second glass substrate (or the stack thereof) may exhibit aneffective viscosity that is between the first viscosity and the secondviscosity at a temperature (T) in a range from about 500° C. to about700° C. The effective viscosity may be determined by equation (1), asfollows:

μ_(eff)(T)=((μ₁(T)t ₁)/(t ₁ +t ₂))+((μ₂(T)t ₂)/(t ₁ +t ₂)),  Equation(1)

where μ₁(T) is the viscosity of the first curved glass substrate attemperature (T), t₁ is the thickness of the first curved glasssubstrate, μ₂(T) is the viscosity of the second curved glass substrateat temperature (T), t₂ is the thickness of the second curved glasssubstrate.

In one or more embodiments, the first curved substrate and the secondcurved substrate (or the first glass substrate and the second glasssubstrate used to form the first curved glass substrate and the secondcurved glass substrate, respectively) may have a sag temperature thatdiffers from one another. As used herein, “sag temperature” means thetemperature at which the viscosity of the glass substrate is about10^(9.9) poises. The sag temperature is determined by fitting theVogel-Fulcher-Tamman (VFT) equation: Log h=A+B/(T−C), where T is thetemperature, A, B and C are fitting constants and h is the dynamicviscosity, to annealing point data measured using the bending beamviscosity (BBV) measurement, to softening point data measured by fiberelongation. In one or more embodiments, the first curved glass substrate(or the first glass substrate used to form the first curved glasssubstrate) may have a first sag temperature and the second curved glasssubstrate (or the second glass substrate used to form the second curvedglass substrate) has a second sag temperature that is greater than thefirst sag temperature. For example, the first sag temperature may be ina range from about 600° C. to about 650° C., from about 600° C. to about640° C., from about 600° C. to about 630° C., from about 600° C. toabout 625° C., from about 600° C. to about 620° C., from about 610° C.to about 650° C., from about 620° C. to about 650° C., from about 625°C. to about 650° C., from about 630° C. to about 650° C., from about620° C. to about 640° C., or from about 625° C. to about 635° C. In oneor more embodiments, the second sag temperature may be greater thanabout 650° C. (e.g., from greater than about 650° C. to about 800° C.,from greater than about 650° C. to about 790° C., from greater thanabout 650° C. to about 780° C., from greater than about 650° C. to about770° C., from greater than about 650° C. to about 760° C., from greaterthan about 650° C. to about 750° C., from greater than about 650° C. toabout 740° C., from greater than about 650° C. to about 740° C., fromgreater than about 650° C. to about 730° C., from greater than about650° C. to about 725° C., from greater than about 650° C. to about 720°C., from greater than about 650° C. to about 710° C., from greater thanabout 650° C. to about 700° C., from greater than about 650° C. to about690° C., from greater than about 650° C. to about 680° C., from about660° C. to about 750° C., from about 670° C. to about 750° C., fromabout 680° C. to about 750° C., from about 690° C. to about 750° C.,from about 700° C. to about 750° C., from about 710° C. to about 750°C., or from about 720° C. to about 750° C.

In one or more embodiments, the difference between the first sagtemperature and the second sag temperature is about 5° C. or greater,about 10° C. or greater, about 15° C. or greater, about 20° C. orgreater, about 25° C. or greater, about 30° C. or greater, or about 35°C. or greater. For example, the difference between the first sagtemperature and the second sag temperature is in a range from about 5°C. to about 150° C., from about 10° C. to about 150° C., from about 15°C. to about 150° C., from about 20° C. to about 150° C., from about 25°C. to about 150° C., from about 30° C. to about 150° C., from about 40°C. to about 150° C., from about 50° C. to about 150° C., from about 60°C. to about 150° C., from about 80° C. to about 150° C., from about 100°C. to about 150° C., from about 5° C. to about 140° C., from about 5° C.to about 120° C., from about 5° C. to about 100° C., from about 5° C. toabout 80° C., from about 5° C. to about 60° C., or from about 5° C. toabout 50° C.

In one or more embodiments, one or both the first sag depth 318 and thesecond sag depth 328 is about 2 mm or greater. For example, one or boththe first sag depth 318 and the second sag depth 328 may be in a rangefrom about 2 mm to about 30 mm, from about 4 mm to about 30 mm, fromabout 5 mm to about 30 mm, from about 6 mm to about 30 mm, from about 8mm to about 30 mm, from about 10 mm to about 30 mm, from about 12 mm toabout 30 mm, from about 14 mm to about 30 mm, from about 15 mm to about30 mm, from about 2 mm to about 28 mm, from about 2 mm to about 26 mm,from about 2 mm to about 25 mm, from about 2 mm to about 24 mm, fromabout 2 mm to about 22 mm, from about 2 mm to about 20 mm, from about 2mm to about 18 mm, from about 2 mm to about 16 mm, from about 2 mm toabout 15 mm, from about 2 mm to about 14 mm, from about 2 mm to about 12mm, from about 2 mm to about 10 mm, from about 2 mm to about 8 mm, fromabout 6 mm to about 20 mm, from about 8 mm to about 18 mm, from about 10mm to about 15 mm, from about 12 mm to about 22 mm, from about 15 mm toabout 25 mm, or from about 18 mm to about 22 mm.

In one or more embodiments, the first sag depth 318 and the second sagdepth 328 are substantially equal to one another. In one or moreembodiments, the first sag depth is within 10% of the second sag depth.For example, the first sag depth is within 9%, within 8%, within 7%,within 6% or within 5% of the second sag depth. For illustration, thesecond sag depth is about 15 mm, and the first sag depth is in a rangefrom about 14.5 mm to about 16.5 mm (or within 10% of the second sagdepth).

In one or more embodiments, the first curved glass substrate and thesecond curved glass substrate comprise a shape deviation therebetweenthe first glass substrate and the second glass substrate of ±5 mm orless as measured by an optical three-dimensional scanner such as theATOS Triple Scan supplied by GOM GmbH, located in Braunschweig, Germany.In one or more embodiments, the shape deviation is measured between thesecond surface 314 and the third surface 322, or between the firstsurface 312 and the fourth surface 324. In one or more embodiments, theshape deviation between the first glass substrate and the second glasssubstrate is about ±4 mm or less, about ±3 mm or less, about ±2 mm orless, about ±1 mm or less, about ±0.8 mm or less, about ±0.6 mm or less,about ±0.5 mm or less, about ±0.4 mm or less, about ±0.3 mm or less,about ±0.2 mm or less, or about ±0.1 mm or less. As used herein, theshape deviation refers to the maximum shape deviation measured on therespective surfaces.

In one or more embodiments, one of or both the first major surface 312and the fourth major surface 324 exhibit minimal optical distortion. Forexample, one of or both the first major surface 312 and the fourth majorsurface 324 exhibit less than about 400 millidiopters, less than about300 millidiopters, or less than about 250 millidiopters, as measured byan optical distortion detector using transmission optics according toASTM 1561. A suitable optical distortion detector is supplied by ISRAVISIION AG, located in Darmstadt, Germany, under the tradenameSCREENSCAN-Faultfinder. In one or more embodiments, one of or both thefirst major surface 312 and the fourth major surface 324 exhibit about190 millidiopters or less, about 180 millidiopters or less, about 170millidiopters or less, about 160 millidiopters or less, about 150millidiopters or less, about 140 millidiopters or less, about 130millidiopters or less, about 120 millidiopters or less, about 110millidiopters or less, about 100 millidiopters or less, about 90millidiopters or less, about 80 millidiopters or less, about 70millidiopters or less, about 60 millidiopters or less, or about 50millidiopters or less. As used herein, the optical distortion refers tothe maximum optical distortion measured on the respective surfaces.

In one or more embodiments, the first major surface or the second majorsurface of the first curved glass substrate exhibits low membranetensile stress. Membrane tensile stress can occur during cooling ofcurved substrates and laminates. As the glass cools, the major surfacesand edge surfaces (orthogonal to the major surfaces) can develop surfacecompression, which is counterbalanced by a central region exhibiting atensile stress. Bending or shaping can introduce additional surfacetension near the edge and causes the central tensile region to approachthe glass surface. Accordingly, membrane tensile stress is the tensilestress measured near the edge (e.g., about 10-25 mm from the edgesurface). In one or more embodiments, the membrane tensile stress at thefirst major surface or the second major surface of the first curvedglass substrate is less than about 7 megaPascals (MPa) as measured by asurface stress meter according to ASTM C1279. An example of such asurface stress meter is supplied by Strainoptic Technologies under thetrademark GASP® (Grazing Angle Surface Polarimeter). In one or moreembodiments, the membrane tensile stress at the first major surface orthe second major surface of the first curved glass substrate is about 6MPa or less, about 5 MPa or less, about 4 MPa or less, or about 3 MPa orless. In one or more embodiments, the lower limit of membrane tensilestress is about 0.01 MPa or about 0.1 MPa. As recited herein, stress isdesignated as either compressive or tensile, with the magnitude of suchstress provided as an absolute value.

In one or more embodiments, the membrane compressive stress at the firstmajor surface or the second major surface of the first curved glasssubstrate is less than about 7 megaPascals (MPa) as measured by asurface stress meter according to ASTM C1279. A surface stress metersuch as the surface stress meter supplied by Strainoptic Technologiesunder the trademark GASP® (Grazing Angle Surface Polarimeter) may beused. In one or more embodiments, the membrane compressive stress at thefirst major surface or the second major surface of the first curvedglass substrate is about 6 MPa or less, about 5 MPa or less, about 4 MPaor less, or about 3 MPa or less. In one or more embodiments, the lowerlimit of membrane compressive stress is about 0.01 MPa or about 0.1 MPa.

In one or more embodiments, the laminate 300 may have a thickness of6.85 mm or less, or 5.85 mm or less, where the thickness comprises thesum of thicknesses of the first curved glass substrate, the secondcurved glass substrate, and the interlayer. In various embodiments, thelaminate may have a thickness in the range of about 1.8 mm to about 6.85mm, or in the range of about 1.8 mm to about 5.85 mm, or in the range ofabout 1.8 mm to about 5.0 mm, or 2.1 mm to about 6.85 mm, or in therange of about 2.1 mm to about 5.85 mm, or in the range of about 2.1 mmto about 5.0 mm, or in the range of about 2.4 mm to about 6.85 mm, or inthe range of about 2.4 mm to about 5.85 mm, or in the range of about 2.4mm to about 5.0 mm, or in the range of about 3.4 mm to about 6.85 mm, orin the range of about 3.4 mm to about 5.85 mm, or in the range of about3.4 mm to about 5.0 mm.

In one or more embodiments, the laminate 300 exhibits radii of curvaturethat is less than 1000 mm, or less than 750 mm, or less than 500 mm, orless than 300 mm. In one or more embodiments, the laminate 300 exhibitsat least one radius of curvature of about 10 m or less, or about 5 m orless along at least one axis. In one or more embodiments, the laminate300 may have a radius of curvature of 5 m or less along at least a firstaxis and along the second axis that is perpendicular to the first axis.In one or more embodiments, the laminate may have a radius of curvatureof 5 m or less along at least a first axis and along the second axisthat is not perpendicular to the first axis.

In one or more embodiments the second curved glass substrate (or thesecond glass substrate used to form the second curved glass substrate)is relatively thin in comparison to the first curved glass substrate (orthe first glass substrate used to form the first curved glasssubstrate). In other words, the first curved glass substrate (or thefirst glass substrate used to form the first curved glass substrate) hasa thickness greater than the second curved glass substrate (or thesecond glass substrate used to form the second curved glass substrate).In one or more embodiments, the first thickness (or the thickness of thefirst glass substrate used to form the first curved glass substrate) ismore than two times the second thickness. In one or more embodiments,the first thickness (or the thickness of the first glass substrate usedto form the first curved glass substrate) is in the range from about 1.5times to about 10 times the second thickness (e.g., from about 1.75times to about 10 times, from about 2 times to about 10 times, fromabout 2.25 times to about 10 times, from about 2.5 times to about 10times, from about 2.75 times to about 10 times, from about 3 times toabout 10 times, from about 3.25 times to about 10 times, from about 3.5times to about 10 times, from about 3.75 times to about 10 times, fromabout 4 times to about 10 times, from about 1.5 times to about 9 times,from about 1.5 times to about 8 times, from about 1.5 times to about 7.5times, from about 1.5 times to about 7 times, from about 1.5 times toabout 6.5 times, from about 1.5 times to about 6 times, from about 1.5times to about 5.5 times, from about 1.5 times to about 5 times, fromabout 1.5 times to about 4.5 times, from about 1.5 times to about 4times, from about 1.5 times to about 3.5 times, from about 2 times toabout 7 times, from about 2.5 times to about 6 times, from about 3 timesto about 6 times).

In one or more embodiments, the first curved glass substrate (or thefirst glass substrate used to form the first curved glass substrate) andthe second curved glass substrate (or the second glass substrate used toform the second curved glass substrate) may have the same thickness. Inone or more specific embodiments, the first curved glass substrate (orthe first glass substrate used to form the first curved glass substrate)is more rigid or has a greater stiffness than the second curved glasssubstrate (or the second glass substrate used to form the second curvedglass substrate), and in very specific embodiments, both the firstcurved glass substrate (or the first glass substrate used to form thefirst curved glass substrate) and the second curved glass substrate (orthe second glass substrate used to form the second curved glasssubstrate) have a thickness in the range of 0.2 mm and 1.6 mm.

In one or more embodiments, either one or both the first thickness (orthe thickness of the first glass substrate used to form the first curvedglass substrate) and the second thickness (or the thickness of thesecond glass substrate used to form the second curved glass substrate)is less than 1.6 mm (e.g., 1.55 mm or less, 1.5 mm or less, 1.45 mm orless, 1.4 mm or less, 1.35 mm or less, 1.3 mm or less, 1.25 mm or less,1.2 mm or less, 1.15 mm or less, 1.1 mm or less, 1.05 mm or less, 1 mmor less, 0.95 mm or less, 0.9 mm or less, 0.85 mm or less, 0.8 mm orless, 0.75 mm or less, 0.7 mm or less, 0.65 mm or less, 0.6 mm or less,0.55 mm or less, 0.5 mm or less, 0.45 mm or less, 0.4 mm or less, 0.35mm or less, 0.3 mm or less, 0.25 mm or less, 0.2 mm or less, 0.15 mm orless, or about 0.1 mm or less). The lower limit of thickness may be 0.1mm, 0.2 mm or 0.3 mm. In some embodiments, either one or both the firstthickness (or the thickness of the first glass substrate used to formthe first curved glass substrate) and the second thickness (or thethickness of the second glass substrate used to form the second curvedglass substrate) is in the range from about 0.1 mm to less than about1.6 mm, from about 0.1 mm to about 1.5 mm, from about 0.1 mm to about1.4 mm, from about 0.1 mm to about 1.3 mm, from about 0.1 mm to about1.2 mm, from about 0.1 mm to about 1.1 mm, from about 0.1 mm to about 1mm, from about 0.1 mm to about 0.9 mm, from about 0.1 mm to about 0.8mm, from about 0.1 mm to about 0.7 mm, from about 0.1 mm, from about 0.2mm to less than about 1.6 mm, from about 0.3 mm to less than about 1.6mm, from about 0.4 mm to less than about 1.6 mm, from about 0.5 mm toless than about 1.6 mm, from about 0.6 mm to less than about 1.6 mm,from about 0.7 mm to less than about 1.6 mm, from about 0.8 mm to lessthan about 1.6 mm, from about 0.9 mm to less than about 1.6 mm, or fromabout 1 mm to about 1.6 mm.

In some embodiments, while one of the first thickness (or the thicknessof the first glass substrate used to form the first curved glasssubstrate) and the second thickness (or the thickness of the secondglass substrate used to form the second curved glass substrate) is lessthan about 1.6 mm, the other of the first thickness (or the thickness ofthe first glass substrate used to form the first curved glass substrate)and the second thickness (or the thickness of the second glass substrateused to form the second curved glass substrate) is about 1.6 mm orgreater. In such embodiments, first thickness (or the thickness of thefirst glass substrate used to form the first curved glass substrate) andthe second thickness (or the thickness of the second glass substrateused to form the second curved glass substrate) differ from one another.For example, the while one of the first thickness (or the thickness ofthe first glass substrate used to form the first curved glass substrate)and the second thickness (or the thickness of the second glass substrateused to form the second curved glass substrate) is less than about 1.6mm, the other of the first thickness (or the thickness of the firstglass substrate used to form the first curved glass substrate) and thesecond thickness (or the thickness of the second glass substrate used toform the second curved glass substrate) is about 1.7 mm or greater,about 1.75 mm or greater, about 1.8 mm or greater, about 1.7 mm orgreater, about 1.7 mm or greater, about 1.7 mm or greater, about 1.85 mmor greater, about 1.9 mm or greater, about 1.95 mm or greater, about 2mm or greater, about 2.1 mm or greater, about 2.2 mm or greater, about2.3 mm or greater, about 2.4 mm or greater, 2.5 mm or greater, 2.6 mm orgreater, 2.7 mm or greater, 2.8 mm or greater, 2.9 mm or greater, 3 mmor greater, 3.2 mm or greater, 3.4 mm or greater, 3.5 mm or greater, 3.6mm or greater, 3.8 mm or greater, 4 mm or greater, 4.2 mm or greater,4.4 mm or greater, 4.6 mm or greater, 4.8 mm or greater, 5 mm orgreater, 5.2 mm or greater, 5.4 mm or greater, 5.6 mm or greater, 5.8 mmor greater, or 6 mm or greater. In some embodiments the first thickness(or the thickness of the first glass substrate used to form the firstcurved glass substrate) or the second thickness (or the thickness of thesecond glass substrate used to form the second curved glass substrate)is in a range from about 1.6 mm to about 6 mm, from about 1.7 mm toabout 6 mm, from about 1.8 mm to about 6 mm, from about 1.9 mm to about6 mm, from about 2 mm to about 6 mm, from about 2.1 mm to about 6 mm,from about 2.2 mm to about 6 mm, from about 2.3 mm to about 6 mm, fromabout 2.4 mm to about 6 mm, from about 2.5 mm to about 6 mm, from about2.6 mm to about 6 mm, from about 2.8 mm to about 6 mm, from about 3 mmto about 6 mm, from about 3.2 mm to about 6 mm, from about 3.4 mm toabout 6 mm, from about 3.6 mm to about 6 mm, from about 3.8 mm to about6 mm, from about 4 mm to about 6 mm, from about 1.6 mm to about 5.8 mm,from about 1.6 mm to about 5.6 mm, from about 1.6 mm to about 5.5 mm,from about 1.6 mm to about 5.4 mm, from about 1.6 mm to about 5.2 mm,from about 1.6 mm to about 5 mm, from about 1.6 mm to about 4.8 mm, fromabout 1.6 mm to about 4.6 mm, from about 1.6 mm to about 4.4 mm, fromabout 1.6 mm to about 4.2 mm, from about 1.6 mm to about 4 mm, fromabout 3.8 mm to about 5.8 mm, from about 1.6 mm to about 3.6 mm, fromabout 1.6 mm to about 3.4 mm, from about 1.6 mm to about 3.2 mm, or fromabout 1.6 mm to about 3 mm.

In one or more specific examples, the first thickness (or the thicknessof the first glass substrate used to form the first curved glasssubstrate) is from about 1.6 mm to about 3 mm, and the second thickness(or the thickness of the second glass substrate used to form the secondcurved glass substrate) is in a range from about 0.1 mm to less thanabout 1.6 mm.

In one or more embodiments, the laminate 300 is substantially free ofvisual distortion as measured by ASTM C1652/C1652M. In specificembodiments, the laminate, the first curved glass substrate and/or thesecond curved glass substrate are substantially free of wrinkles ordistortions that can be visually detected by the naked eye, according toASTM C1652/C1652M.

In one or more embodiments, the first major surface 312 or the secondmajor surface 314 comprises a surface compressive stress of less than 3MPa as measured by a surface stress meter, such as the surface stressmeter commercially available under the tradename FSM-6000, from OriharaIndustrial Co., Ltd. (Japan) (“FSM”). In some embodiments, the firstcurved glass substrate is unstrengthened as will be described herein(but may optionally be annealed), and exhibits a surface compressivestress of less than about 3 MPa, or about 2.5 MPa or less, 2 MPa orless, 1.5 MPa or less, 1 MPa or less, or about 0.5 MPa or less. In someembodiments, such surface compressive stress ranges are present on boththe first major surface and the second major surface.

In one or more embodiments, the first and second glass substrates usedto form the first curved glass substrate and second curved substrate areprovided as a substantially planar sheet 500 prior to being co-shaped toform a first curved glass substrate and second curved glass substrate,as shown in FIG. 5. The substantially planar sheets may include firstand second major opposing surfaces 502, 504 and minor opposing surfaces506, 507. In some instances, one or both of the first glass substrateand the second glass substrate used to form the first curved glasssubstrate and second curved substrate may have a 3D or 2.5D shape thatdoes not exhibit the sag depth desired and will eventually be formedduring the co-shaping process and present in the resulting laminate.Additionally or alternatively, the thickness of the one or both of thefirst curved glass substrate (or the first glass substrate used to formthe first curved glass substrate) and the second curved glass substrate(or the second glass substrate used to form the second curved glasssubstrate) may be constant along one or more dimension or may vary alongone or more of its dimensions for aesthetic and/or functional reasons.For example, the edges of one or both of the first curved glasssubstrate (or the first glass substrate used to form the first curvedglass substrate) and the second curved glass substrate (or the secondglass substrate used to form the second curved glass substrate) may bethicker as compared to more central regions of the glass substrate.

The length, width and thickness dimensions of the first curved glasssubstrate (or the first glass substrate used to form the first curvedglass substrate) and the second curved glass substrate (or the secondglass substrate used to form the second curved glass substrate) may alsovary according to the article application or use. In one or moreembodiments, the first curved glass substrate 310 (or the first glasssubstrate used to form the first curved glass substrate) includes afirst length and a first width (the first thickness is orthogonal boththe first length and the first width), and the second curved glasssubstrate 320 (or the second glass substrate used to form the secondcurved glass substrate) includes a second length and a second widthorthogonal the second length (the second thickness is orthogonal boththe second length and the second width). In one or more embodiments,either one of or both the first length and the first width is about 0.25meters (m) or greater. For example, the first length and/or the secondlength may be in a range from about 1 m to about 3 m, from about 1.2 mto about 3 m, from about 1.4 m to about 3 m, from about 1.5 m to about 3m, from about 1.6 m to about 3 m, from about 1.8 m to about 3 m, fromabout 2 m to about 3 m, from about 1 m to about 2.8 m, from about 1 m toabout 2.8 m, from about 1 m to about 2.8 m, from about 1 m to about 2.8m, from about 1 m to about 2.6 m, from about 1 m to about 2.5 m, fromabout 1 m to about 2.4 m, from about 1 m to about 2.2 m, from about 1 mto about 2 m, from about 1 m to about 1.8 m, from about 1 m to about 1.6m, from about 1 m to about 1.5 m, from about 1.2 m to about 1.8 m orfrom about 1.4 m to about 1.6 m.

For example, the first width and/or the second width may be in a rangefrom about 0.5 m to about 2 m, from about 0.6 m to about 2 m, from about0.8 m to about 2 m, from about 1 m to about 2 m, from about 1.2 m toabout 2 m, from about 1.4 m to about 2 m, from about 1.5 m to about 2 m,from about 0.5 m to about 1.8 m, from about 0.5 m to about 1.6 m, fromabout 0.5 m to about 1.5 m, from about 0.5 m to about 1.4 m, from about0.5 m to about 1.2 m, from about 0.5 m to about 1 m, from about 0.5 m toabout 0.8 m, from about 0.75 m to about 1.5 m, from about 0.75 m toabout 1.25 m, or from about 0.8 m to about 1.2 m.

In one or more embodiments, the second length is within 5% of the firstlength (e.g., about 5% or less, about 4% or less, about 3% or less, orabout 2% or less). For example if the first length is 1.5 m, the secondlength may be in a range from about 1.425 m to about 1.575 m and stillbe within 5% of the first length. In one or more embodiments, the secondwidth is within 5% of the first width (e.g., about 5% or less, about 4%or less, about 3% or less, or about 2% or less). For example if thefirst width is 1 m, the second width may be in a range from about 1.05 mto about 0.95 m and still be within 5% of the first width.

In some embodiments, one or both of the first curved glass substrate (orthe first glass substrate used to form the first curved glass substrate)and the second curved glass substrate (or the second glass substrateused to form the second curved glass substrate) 500A may have a wedgedshape in which the thickness at one minor surface 506A is greater thanthe thickness at an opposing minor surface 507A, as illustrated in FIG.6. Where the thickness varies, the thickness ranges disclosed herein arethe maximum thickness between the major surfaces.

In one or more embodiments, the first curved glass substrate (or thefirst glass substrate used to form the first curved glass substrate) andthe second curved glass substrate (or the second glass substrate used toform the second curved glass substrate) may have a refractive index inthe range from about 1.2 to about 1.8, from about 1.2 to about 1.75,from about 1.2 to about 1.7, from about 1.2 to about 1.65, from about1.2 to about 1.6, from about 1.2 to about 1.55, from about 1.25 to about1.8, from about 1.3 to about 1.8, from about 1.35 to about 1.8, fromabout 1.4 to about 1.8, from about 1.45 to about 1.8, from about 1.5 toabout 1.8, from about 1.55 to about 1.8, of from about 1.45 to about1.55. As used herein, the refractive index values are with respect to awavelength of 550 nm.

In one or more embodiments, the first curved glass substrate (or thefirst glass substrate used to form the first curved glass substrate) andthe second curved glass substrate (or the second glass substrate used toform the second curved glass substrate) may be characterized by themanner in which it is formed. For instance, one of or both the firstcurved glass substrate (or the first glass substrate used to form thefirst curved glass substrate) and the second curved glass substrate (orthe second glass substrate used to form the second curved glasssubstrate) may be characterized as float-formable (i.e., formed by afloat process), down-drawable and, in particular, fusion-formable orslot-drawable (i.e., formed by a down draw process such as a fusion drawprocess or a slot draw process).

One of or both the first curved glass substrate (or the first glasssubstrate used to form the first curved glass substrate) and the secondcurved glass substrate (or the second glass substrate used to form thesecond curved glass substrate) described herein may be formed by a floatprocess. A float-formable glass substrate may be characterized by smoothsurfaces and uniform thickness is made by floating molten glass on a bedof molten metal, typically tin. In an example process, molten glass thatis fed onto the surface of the molten tin bed forms a floating glassribbon. As the glass ribbon flows along the tin bath, the temperature isgradually decreased until the glass ribbon solidifies into a solid glasssubstrate that can be lifted from the tin onto rollers. Once off thebath, the glass substrate can be cooled further and annealed to reduceinternal stress.

One of or both the first curved glass substrate (or the first glasssubstrate used to form the first curved glass substrate) and the secondcurved glass substrate (or the second glass substrate used to form thesecond curved glass substrate) may be formed by a down-draw process.Down-draw processes produce glass substrates having a substantiallyuniform thickness that possess relatively pristine surfaces. Because theaverage flexural strength of the glass substrates is generallycontrolled by the amount and size of surface flaws, a pristine surfacethat has had minimal contact has a higher initial strength. In addition,down drawn glass substrates have a very flat, smooth surface that can beused in its final application without costly grinding and polishing.

One of or both the first curved glass substrate (or the first glasssubstrate used to form the first curved glass substrate) and the secondcurved glass substrate (or the second glass substrate used to form thesecond curved glass substrate) may be described as fusion-formable(i.e., formable using a fusion draw process). The fusion process uses adrawing tank that has a channel for accepting molten glass raw material.The channel has weirs that are open at the top along the length of thechannel on both sides of the channel. When the channel fills with moltenmaterial, the molten glass overflows the weirs. Due to gravity, themolten glass flows down the outside surfaces of the drawing tank as twoflowing glass films. These outside surfaces of the drawing tank extenddown and inwardly so that they join at an edge below the drawing tank.The two flowing glass films join at this edge to fuse and form a singleflowing glass substrate. The fusion draw method offers the advantagethat, because the two glass films flowing over the channel fusetogether, neither of the outside surfaces of the resulting glasssubstrate comes in contact with any part of the apparatus. Thus, thesurface properties of the fusion drawn glass substrate are not affectedby such contact.

One of or both the first curved glass substrate (or the first glasssubstrate used to form the first curved glass substrate) and the secondcurved glass substrate (or the second glass substrate used to form thesecond curved glass substrate) described herein may be formed by a slotdraw process. The slot draw process is distinct from the fusion drawmethod. In slow draw processes, the molten raw material glass isprovided to a drawing tank. The bottom of the drawing tank has an openslot with a nozzle that extends the length of the slot. The molten glassflows through the slot/nozzle and is drawn downward as a continuousglass substrate and into an annealing region.

In one or more embodiments, one of or both the first curved glasssubstrate (or the first glass substrate used to form the first curvedglass substrate) and the second curved glass substrate (or the secondglass substrate used to form the second curved glass substrate) andsecond substrate may be glass (e.g., soda lime glass, alkalialuminosilicate glass, alkali containing borosilicate glass and/oralkali aluminoborosilicate glass) or glass-ceramic. In some embodiments,one of or both the first curved glass substrate (or the first glasssubstrate used to form the first curved glass substrate) and the secondcurved glass substrate (or the second glass substrate used to form thesecond curved glass substrate) described herein may exhibit an amorphousmicrostructure and may be substantially free of crystals orcrystallites. In other words, the glass substrates of certainembodiments exclude glass-ceramic materials. In some embodiments, one ofor both the first curved glass substrate (or the first glass substrateused to form the first curved glass substrate) and the second curvedglass substrate (or the second glass substrate used to form the secondcurved glass substrate) is a glass-ceramic. Examples of suitableglass-ceramics include Li₂O—Al₂O₃—SiO₂ system (i.e. LAS-System)glass-ceramics, MgO—Al₂O₃—SiO₂ system (i.e. MAS-System) glass-ceramics,and glass-ceramics including crystalline phases of any one or more ofmullite, spinel, α-quartz, β-quartz solid solution, petalite, lithiumdissilicate, β-spodumene, nepheline, and alumina. Such substratesincluding glass-ceramic materials may be strengthened as describedherein.

In one or more embodiments, one of or both the first curved glasssubstrate (or the first glass substrate used to form the first curvedglass substrate) and the second curved glass substrate (or the secondglass substrate used to form the second curved glass substrate) exhibitsa total solar transmittance of about 92% or less, over a wavelengthrange from about 300 nm to about 2500 nm, when the glass substrate has athickness of 0.7 mm. For example, the one of or both the first andsecond glass substrates exhibits a total solar transmittance in a rangefrom about 60% to about 92%, from about 62% to about 92%, from about 64%to about 92%, from about 65% to about 92%, from about 66% to about 92%,from about 68% to about 92%, from about 70% to about 92%, from about 72%to about 92%, from about 60% to about 90%, from about 60% to about 88%,from about 60% to about 86%, from about 60% to about 85%, from about 60%to about 84%, from about 60% to about 82%, from about 60% to about 80%,from about 60% to about 78%, from about 60% to about 76%, from about 60%to about 75%, from about 60% to about 74%, or from about 60% to about72%.

In one or more embodiments, one or both the first curved glass substrate(or the first glass substrate used to form the first curved glasssubstrate) and the second curved glass substrate (or the second glasssubstrate used to form the second curved glass substrate) are tinted. Insuch embodiments, the first curved glass substrate (or the first glasssubstrate used to form the first curved glass substrate) may comprise afirst tint and the second curved glass substrate (or the second glasssubstrate used to form the second curved glass substrate) comprises asecond tint that differs from the first tint, in the CIE L*a*b* (CIELAB)color space. In one or more embodiments, the first tint and the secondtint are the same. In one or more specific embodiments, the first curvedglass substrate comprises a first tint, and the second curved glasssubstrate is not tinted. In one or more specific embodiments, the secondcurved glass substrate comprises a second tint, and the first curvedglass substrate is not tinted.

In one or embodiments, the one of or both the first curved glasssubstrate (or the first glass substrate used to form the first curvedglass substrate) and the second curved glass substrate (or the secondglass substrate used to form the second curved glass substrate) exhibitsan average transmittance in the range from about 75% to about 85%, at athickness of 0.7 mm or 1 mm, over a wavelength range from about 380 nmto about 780 nm. In some embodiments, the average transmittance at thisthickness and over this wavelength range may be in a range from about75% to about 84%, from about 75% to about 83%, from about 75% to about82%, from about 75% to about 81%, from about 75% to about 80%, fromabout 76% to about 85%, from about 77% to about 85%, from about 78% toabout 85%, from about 79% to about 85%, or from about 80% to about 85%.In one or more embodiments, the one of or both the first curved glasssubstrate (or the first glass substrate used to form the first curvedglass substrate) and the second curved glass substrate (or the secondglass substrate used to form the second curved glass substrate) exhibitsT_(uv-380) or T_(uv-400) of 50% or less (e.g., 49% or less, 48% or less,45% or less, 40% or less, 30% or less, 25% or less, 23% or less, 20% orless, or 15% or less), at a thickness of 0.7 mm or 1 mm, over awavelength range from about 300 nm to about 400 nm.

In one or more embodiments, the one of or both the first curved glasssubstrate (or the first glass substrate used to form the first curvedglass substrate) and the second curved glass substrate (or the secondglass substrate used to form the second curved glass substrate) may bestrengthened to include compressive stress that extends from a surfaceto a depth of compression (DOC). The compressive stress regions arebalanced by a central portion exhibiting a tensile stress. At the DOC,the stress crosses from a positive (compressive) stress to a negative(tensile) stress.

In one or more embodiments, such strengthened glass substrates may bechemically strengthened, mechanically strengthened or thermallystrengthened. In some embodiments, the strengthened glass substrate maybe chemically and mechanically strengthened, mechanically and thermallystrengthened, chemically and thermally strengthened or chemically,mechanically and thermally strengthened. In one or more specificembodiments, the second curved glass substrate (or the second glasssubstrate used to form the second curved glass substrate) isstrengthened and the first curved glass substrate (or the first glasssubstrate used to form the first curved glass substrate) isunstrengthened but optionally annealed. In one or more embodiments, thefirst curved glass substrate (or the first glass substrate used to formthe first curved glass substrate) is strengthened. In specificembodiments, both the first curved glass substrate (or the first glasssubstrate used to form the first curved glass substrate) and the secondcurved glass substrate (or the second glass substrate used to form thesecond curved glass substrate) are strengthened. In one or moreembodiments, where one or both the glass substrates are chemicallyand/or thermally strengthened, such chemical and/or thermalstrengthening is performed on the curved glass substrate (i.e., aftershaping). In some embodiments, such glass substrates may be optionallymechanically strengthened before shaping. In one or more embodiments,where one or both the glass substrates are mechanically strengthened(and optionally combined with one or more other strengthening methods),such mechanical strengthening occurs before shaping.

In one or more embodiments, the one of or both the first curved glasssubstrate (or the first glass substrate used to form the first curvedglass substrate) and the second curved glass substrate (or the secondglass substrate used to form the second curved glass substrate) may bestrengthened mechanically by utilizing a mismatch of the coefficient ofthermal expansion between portions of the article to create acompressive stress region and a central region exhibiting a tensilestress. The DOC in such mechanically strengthened substrates istypically the thickness of the outer portions of the glass substratehaving one coefficient of thermal expansion (i.e., the point at whichthe glass substrate coefficient of thermal expansion changes from one toanother value).

In some embodiments, the one of or both the first curved glass substrate(or the first glass substrate used to form the first curved glasssubstrate) and the second curved glass substrate (or the second glasssubstrate used to form the second curved glass substrate) may bestrengthened thermally by heating the glass substrate to a temperaturebelow the glass transition point and then rapidly thermally quenching,or lowering its temperature. As noted above, in one or more embodiments,where one or both the glass substrates are thermally strengthened, suchthermal strengthening is performed on the curved glass substrate (i.e.,after shaping).

In one or more embodiments, the one of or both the first curved glasssubstrate (or the first glass substrate used to form the first curvedglass substrate) and the second curved glass substrate (or the secondglass substrate used to form the second curved glass substrate) may bechemically strengthening by ion exchange. As noted above, in one or moreembodiments, where one or both the glass substrates are chemicallystrengthened, such chemical strengthening is performed on the curvedglass substrate (i.e., after shaping). In the ion exchange process, ionsat or near the surface of the glass substrate are replaced by—orexchanged with—larger ions having the same valence or oxidation state.In those embodiments in which the glass substrate comprises acomposition including at least one alkali metal oxide as measured on anoxide basis (e.g., Li₂O, Na₂O, K₂O, Rb₂O, or Cs₂O), ions in the surfacelayer of the article and the larger ions are monovalent alkali metalcations, such as Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺. Alternatively, monovalentcations in the surface layer may be replaced with monovalent cationsother than alkali metal cations, such as Ag⁺ or the like. In suchembodiments, the monovalent ions (or cations) exchanged into the glasssubstrate generate a compressive stress on the surface portions,balanced by a tensile stress in the central portions.

Ion exchange processes are typically carried out by immersing a glasssubstrate in a molten salt bath (or two or more molten salt baths)containing the larger ions to be exchanged with the smaller ions in theglass substrate. It should be noted that aqueous salt baths may also beutilized. In addition, the composition of the bath(s) may include morethan one type of larger ion (e.g., Na+ and K+) or a single larger ion.It will be appreciated by those skilled in the art that parameters forthe ion exchange process, including, but not limited to, bathcomposition and temperature, immersion time, the number of immersions ofthe glass substrate in a salt bath (or baths), use of multiple saltbaths, additional steps such as annealing, washing, and the like, aregenerally determined by the composition of the glass substrate(including the structure of the article and any crystalline phasespresent) and the desired DOC and CS of the glass substrate that resultsfrom strengthening. Exemplary molten bath composition may includenitrates, sulfates, and chlorides of the larger alkali metal ion.Typical nitrates include KNO₃, NaNO₃, LiNO₃, NaSO₄ and combinationsthereof. The temperature of the molten salt bath typically is in a rangefrom about 380° C. up to about 450° C., while immersion times range fromabout 15 minutes up to about 100 hours depending on glass substratethickness, bath temperature and glass (or monovalent ion) diffusivity.However, temperatures and immersion times different from those describedabove may also be used.

In one or more embodiments, the glass substrate may be immersed in amolten salt bath of 100% NaNO₃, 100% KNO₃, or a combination of NaNO₃ andKNO₃ having a temperature from about 370° C. to about 480° C. In someembodiments, the glass substrate may be immersed in a molten mixed saltbath including from about 5% to about 90% KNO₃ and from about 10% toabout 95% NaNO₃. In one or more embodiments, the glass substrate may beimmersed in a second bath, after immersion in a first bath. The firstand second baths may have different compositions and/or temperaturesfrom one another. The immersion times in the first and second baths mayvary. For example, immersion in the first bath may be longer than theimmersion in the second bath.

In one or more embodiments, the glass substrate may be immersed in amolten, mixed salt bath including NaNO₃ and KNO₃ (e.g., 49%/51%,50%/50%, 51%/49%) having a temperature less than about 420° C. (e.g.,about 400° C. or about 380° C.). for less than about 5 hours, or evenabout 4 hours or less.

Ion exchange conditions can be tailored to provide a “spike” or toincrease the slope of the stress profile at or near the surface of theresulting glass substrate. The spike may result in a greater surface CSvalue. This spike can be achieved by single bath or multiple baths, withthe bath(s) having a single composition or mixed composition, due to theunique properties of the glass compositions used in the glass substratesdescribed herein.

In one or more embodiments, where more than one monovalent ion isexchanged into the glass substrate, the different monovalent ions mayexchange to different depths within the glass substrate (and generatedifferent magnitude stresses within the glass substrate at differentdepths). The resulting relative depths of the stress-generating ions canbe determined and cause different characteristics of the stress profile.

CS is measured using those means known in the art, such as by surfacestress meter (FSM) using commercially available instruments such as theFSM-6000, manufactured by Orihara Industrial Co., Ltd. (Japan). Surfacestress measurements rely upon the accurate measurement of the stressoptical coefficient (SOC), which is related to the birefringence of theglass. SOC in turn is measured by those methods that are known in theart, such as fiber and four point bend methods, both of which aredescribed in ASTM standard C770-98 (2013), entitled “Standard TestMethod for Measurement of Glass Stress-Optical Coefficient,” thecontents of which are incorporated herein by reference in theirentirety, and a bulk cylinder method. As used herein CS may be the“maximum compressive stress” which is the highest compressive stressvalue measured within the compressive stress layer. In some embodiments,the maximum compressive stress is located at the surface of the glasssubstrate. In other embodiments, the maximum compressive stress mayoccur at a depth below the surface, giving the compressive profile theappearance of a “buried peak.”

DOC may be measured by FSM or by a scattered light polariscope (SCALP)(such as the SCALP-04 scattered light polariscope available fromGlasstress Ltd., located in Tallinn Estonia), depending on thestrengthening method and conditions. When the glass substrate ischemically strengthened by an ion exchange treatment, FSM or SCALP maybe used depending on which ion is exchanged into the glass substrate.Where the stress in the glass substrate is generated by exchangingpotassium ions into the glass substrate, FSM is used to measure DOC.Where the stress is generated by exchanging sodium ions into the glasssubstrate, SCALP is used to measure DOC. Where the stress in the glasssubstrate is generated by exchanging both potassium and sodium ions intothe glass, the DOC is measured by SCALP, since it is believed theexchange depth of sodium indicates the DOC and the exchange depth ofpotassium ions indicates a change in the magnitude of the compressivestress (but not the change in stress from compressive to tensile); theexchange depth of potassium ions in such glass substrates is measured byFSM. Central tension or CT is the maximum tensile stress and is measuredby SCALP.

In one or more embodiments, the first curved glass substrate (or thefirst glass substrate used to form the first curved glass substrate) andthe second curved glass substrate (or the second glass substrate used toform the second curved glass substrate) may be strengthened to exhibit aDOC that is described a fraction of the thickness t of the glasssubstrate (as described herein). For example, in one or moreembodiments, the DOC may be equal to or greater than about 0.03t, equalto or greater than about 0.035t, equal to or greater than about 0.04t,equal to or greater than about 0.045t, equal to or greater than about0.05t, equal to or greater than about 0.1t, equal to or greater thanabout 0.11t, equal to or greater than about 0.12t, equal to or greaterthan about 0.13t, equal to or greater than about 0.14t, equal to orgreater than about 0.15t, equal to or greater than about 0.16t, equal toor greater than about 0.17t, equal to or greater than about 0.18t, equalto or greater than about 0.19t, equal to or greater than about 0.2t,equal to or greater than about 0.21t. In some embodiments. The DOC maybe in a range from about 0.03t to about 0.25t, from about 0.04t to about0.25 t, from about 0.05t to about 0.25 t, from about 0.06t to about 0.25t, from about 0.07t to about 0.25 t, from about 0.08t to about 0.25t,from about 0.09t to about 0.25t, from about 0.18t to about 0.25t, fromabout 0.11t to about 0.25t, from about 0.12t to about 0.25t, from about0.13t to about 0.25t, from about 0.14t to about 0.25t, from about 0.15tto about 0.25t, from about 0.08t to about 0.24t, from about 0.08t toabout 0.23t, from about 0.08t to about 0.22t, from about 0.08t to about0.21t, from about 0.08t to about 0.2t, from about 0.08t to about 0.19t,from about 0.08t to about 0.18t, from about 0.08t to about 0.17t, fromabout 0.08t to about 0.16t, or from about 0.08t to about 0.15t. In someinstances, the DOC may be about 20 μm or less. In one or moreembodiments, the DOC may be about 40 μm or greater (e.g., from about 40μm to about 300 μm, from about 50 μm to about 300 μm, from about 60 μmto about 300 μm, from about 70 μm to about 300 μm, from about 80 μm toabout 300 μm, from about 90 μm to about 300 μm, from about 100 μm toabout 300 μm, from about 110 μm to about 300 μm, from about 120 μm toabout 300 μm, from about 140 μm to about 300 μm, from about 150 μm toabout 300 μm, from about 40 μm to about 290 μm, from about 40 μm toabout 280 μm, from about 40 μm to about 260 μm, from about 40 μm toabout 250 μm, from about 40 μm to about 240 μm, from about 40 μm toabout 230 μm, from about 40 μm to about 220 μm, from about 40 μm toabout 210 μm, from about 40 μm to about 200 μm, from about 40 μm toabout 180 μm, from about 40 μm to about 160 μm, from about 40 μm toabout 150 μm, from about 40 μm to about 140 μm, from about 40 μm toabout 130 μm, from about 40 μm to about 120 μm, from about 40 μm toabout 110 μm, or from about 40 μm to about 100 μm.

In one or more embodiments, the strengthened glass substrate may have aCS (which may be found at the surface or a depth within the glasssubstrate) of about 100 MPa or greater, about 150 MPa or greater, about200 MPa or greater, about 300 MPa or greater, about 400 MPa or greater,about 500 MPa or greater, about 600 MPa or greater, about 700 MPa orgreater, about 800 MPa or greater, about 900 MPa or greater, about 930MPa or greater, about 1000 MPa or greater, or about 1050 MPa or greater.

In one or more embodiments, the strengthened glass substrate may have amaximum tensile stress or central tension (CT) of about 20 MPa orgreater, about 30 MPa or greater, about 40 MPa or greater, about 45 MPaor greater, about 50 MPa or greater, about 60 MPa or greater, about 70MPa or greater, about 75 MPa or greater, about 80 MPa or greater, orabout 85 MPa or greater. In some embodiments, the maximum tensile stressor central tension (CT) may be in a range from about 40 MPa to about 100MPa.

In one or more embodiments, the first curved glass substrate (or thefirst glass substrate used to form the first curved glass substrate) andthe second curved glass substrate (or the second glass substrate used toform the second curved glass substrate) comprise one of soda limesilicate glass, an alkali aluminosilicate glass, alkali containingborosilicate glass, alkali aluminophosphosilicate glass, or alkalialuminoborosilicate glass. In one or more embodiments, one of the firstcurved glass substrate (or the first glass substrate used to form thefirst curved glass substrate) and the second curved glass substrate (orthe second glass substrate used to form the second curved glasssubstrate) is a soda lime silicate glass, while the other of the firstcurved glass substrate (or the first glass substrate used to form thefirst curved glass substrate) and the second curved glass substrate (orthe second glass substrate used to form the second curved glasssubstrate) is an alkali aluminosilicate glass, alkali containingborosilicate glass, alkali aluminophosphosilicate glass, or alkalialuminoborosilicate glass.

In one or more embodiments, the interlayer used herein (e.g., 330) mayinclude a single layer or multiple layers. The interlayer (or layersthereof) may be formed polymers such as polyvinyl butyral (PVB),acoustic PBV (APVB), ionomers, ethylene-vinyl acetate (EVA) andthermoplastic polyurethane (TPU), polyester (PE), polyethyleneterephthalate (PET) and the like. The thickness of the interlayer may bein the range from about 0.5 mm to about 2.5 mm, from about 0.8 mm toabout 2.5 mm, from about 1 mm to about 2.5 mm or from about 1.5 mm toabout 2.5 mm. The interlayer may also have a non-uniform thickness, orwedge shape, from one edge to the other edge of the laminate.

In one more embodiments, the laminate (and/or one of or both the firstcurved glass substrate and the second curved glass substrate) exhibits acomplexly curved shape. As used herein “complex curve” and “complexlycurved” mean a non-planar shape having curvature along two orthogonalaxes that are different from one another. Examples of complexly curvedshapes includes having simple or compound curves, also referred to asnon-developable shapes, which include but are not limited to spherical,aspherical, and toroidal. The complexly curved laminates according toembodiments may also include segments or portions of such surfaces, orbe comprised of a combination of such curves and surfaces. In one ormore embodiments, a laminate may have a compound curve including a majorradius and a cross curvature. A complexly curved laminate according toone or more embodiments may have a distinct radius of curvature in twoindependent directions. According to one or more embodiments, complexlycurved laminates may thus be characterized as having “cross curvature,”where the laminate is curved along an axis (i.e., a first axis) that isparallel to a given dimension and also curved along an axis (i.e., asecond axis) that is perpendicular to the same dimension. The curvatureof the laminate can be even more complex when a significant minimumradius is combined with a significant cross curvature, and/or depth ofbend. Some laminates may also include bending along axes that are notperpendicular to one another. As a non-limiting example, thecomplexly-curved laminate may have length and width dimensions of 0.5 mby 1.0 m and a radius of curvature of 2 to 2.5 m along the minor axis,and a radius of curvature of 4 to 5 m along the major axis. In one ormore embodiments, the complexly-curved laminate may have a radius ofcurvature of 5 m or less along at least one axis. In one or moreembodiments, the complexly-curved laminate may have a radius ofcurvature of 5 m or less along at least a first axis and along thesecond axis that is perpendicular to the first axis. In one or moreembodiments, the complexly-curved laminate may have a radius ofcurvature of 5 m or less along at least a first axis and along thesecond axis that is not perpendicular to the first axis.

The laminate of any one of the preceding claims, wherein the laminatecomprises automotive glazing or architectural glazing.

A second aspect of this disclosure pertains to a vehicle that includes alaminate according to one or more embodiments described herein. Forexample, as shown in FIG. 7 shows a vehicle 600 comprising a body 610defining an interior, at least one opening 620 in communication with theinterior, and a glazing disposed in the opening, wherein the windowcomprises a laminate 630, according to one or more embodiments describedherein. In one or more embodiments, the laminate is complexly curved.The laminate 630 may form the sidelights, windshields, rear windows,rearview mirrors, and sunroofs in the vehicle. In some embodiments, thelaminate 630 may form an interior partition (not shown) within theinterior of the vehicle, or may be disposed on an exterior surface ofthe vehicle and form an engine block cover, headlight cover, taillightcover, or pillar cover. In one or more embodiments, the vehicle mayinclude an interior surface (not shown, but may include door trim, seatbacks, door panels, dashboards, center consoles, floor boards, andpillars), and the laminate or glass article described herein is disposedon the interior surface. In one or more embodiment, the interior surfaceincludes a display and the glass layer is disposed over the display. Asused herein, vehicle includes automobiles, motorcycles, rolling stock,locomotive, boats, ships, airplanes, helicopters, drones, space craftand the like.

Another aspect of this disclosure pertains to an architecturalapplication that includes the laminates described herein. In someembodiments, the architectural application includes balustrades, stairs,decorative panels or covering for walls, columns, partitions, elevatorcabs, household appliances, windows, furniture, and other applications,formed at least partially using a laminate or glass article according toone or more embodiments.

In one or more embodiments, the laminate is positioned within a vehicleor architectural application such that the second curved glass substratefaces the interior of the vehicle or the interior of a building or room,such that the second curved glass substrate is adjacent to the interior(and the first curved glass substrate is adjacent the exterior). In someembodiments, the second curved glass substrate is in direct contact withthe interior (i.e., the fourth surface 324 of the second curved glasssubstrate glass article facing the interior is bare and is free of anycoatings). In one or more embodiments, the first surface 312 of thefirst curved glass substrate is bare and is free of any coatings. In oneor more embodiments, the laminate is positioned within a vehicle orarchitectural application such that the second curved glass substratefaces the exterior of the vehicle or the exterior of a building or room,such that the second first curved glass substrate is adjacent to theexterior (and the first curved glass substrate is adjacent theinterior). In some embodiments, the second curved glass substrate of thelaminate is in direct contact with the exterior (i.e., the surface ofthe second curved glass substrate facing the exterior is bare and isfree of any coatings).

In one or more embodiments, referring to FIG. 3, both the first surface312 and the fourth surface 324 is bare and substantially free of anycoatings. In some embodiment one or both the edge portions of the firstsurface 312 and the fourth surface 324 may include a coating while thecentral portions are bare and substantially free of any coatings.Optionally, one or both the first surface 312 and the fourth surface 324includes a coating or surface treatment (e.g., antireflective coating,anti-glare coating or surface, easy-to-clean surface, ink decoration,conductive coatings etc.). In one or more embodiments, the laminateincludes one or more conductive coatings on one of or both the secondsurface 312 or the third surface 322 adjacent the interlayer 330.

In one or more embodiments, referring to FIG. 3A, both the first surface322 and the fourth surface 314 is bare and substantially free of anycoatings. In some embodiment one or both the edge portions of the firstsurface 322 and the fourth surface 314 may include a coating while thecentral portions are bare and substantially free of any coatings.Optionally, one or both the first surface 322 and the fourth surface 314includes a coating or surface treatment (e.g., antireflective coating,anti-glare coating or surface, easy-to-clean surface, ink decoration,conductive coatings etc.). In one or more embodiments, the laminateincludes one or more conductive coatings on one of or both the secondsurface 324 or the third surface 312 adjacent the interlayer 330.

A third aspect of this disclosure pertains to a method of forming acurved laminate, such as the embodiments of the curved laminatesdescribed herein. In one or more embodiments, the method includesforming a stack comprising a first glass substrate according to one ormore embodiments, and a second glass substrate according to one or moreembodiments, and heating the stack and co-shaping the stack to form aco-shaped stack. In one or more embodiments, the second glass substrateis disposed on the first glass substrate to form the stack. In one ormore embodiments, the first glass substrate is disposed on the secondglass substrate to form the stack.

Heating the stack may include placing the stack in a dynamic furnacesuch as a lehr furnace or a static furnace. An example of a lehr furnace700 is shown in FIG. 8. In a dynamic furnace such as a lehr furnace, thestack is introduced in a first module 702 and then conveyed through aseries of modules 702, 704, 706, 708, 710, 712, having sequentiallyincreasing temperatures until reaching a maximum temperature in module714. This maximum temperature is referred to as the set point of thefurnace. In module 716, the stack is co-shaped. In some embodiments,heat is applied in module 716, but may not be required. The stack isthen conveyed through module 718 to a series of modules 720, 722, 724,726, 728, 730, 732 with sequentially decreasing temperature that permitgradual cooling of the stack until it reaches module 734. The durationof time for which the stack is present in each module is also specified(e.g., in a range from about 30 seconds to 500 seconds). In one or moreembodiments, module 704 is controlled to have a temperature in a rangefrom about 225° C. to about 275° C., module 706 is controlled to have atemperature in a range from about 400° C. to about 460° C., module 708is controlled to have a temperature in a range from about 530° C. toabout 590° C., module 710 is controlled to have a temperature in a rangefrom about 580° C. to about 640° C., module 712 is controlled to have atemperature in a range from about 590° C. to about 650° C., and module714 is controlled to have a temperature in a range from about 600° C. toabout 680° C. In typical furnaces, the temperature of the glasssubstrates is less than the temperature at which the module iscontrolled. For example, the difference between the glass substratetemperature and the controlled module temperature may be in a range fromabout 10° C. to 20° C.

In one or more embodiments, the stack comprises opposing major surfaceseach comprising a central portion and an edge portion surrounding thecentral portion. In one or more embodiments, the co-shaped stackincludes a first curved glass substrate having a first sag depth and asecond curved glass substrate each having a second sag depth, whereinthe first sag depth and the second sag depth are greater than 2 mm andwithin 10% of one another.

In one or more embodiments, the first glass substrate (prior to heatingand co-shaping) includes a first viscosity (poises) and a first sagtemperature and the second glass substrate includes a second viscositythat greater than or equal to 10 times the first viscosity and a secondsag temperature that differs from the first sag temperature by about 30°C. or more (e.g., 35° C. or more, 40° C. or more, 45° C. or more, 50° C.or more, 55° C. or more, or 60° C. or more).

In one or more embodiments, heating the stack comprises heating thestack to a temperature different from the first sag temperature and thesecond sag temperature. In some embodiments, heating the stack comprisesheating the stack to a temperature between the first sag temperature andthe second sag temperature (e.g., from about 630° C. to about 665° C.,from about 630° C. to about 660° C., from about 630° C. to about 655°C., from about 630° C. to about 650° C., from about 630° C. to about645° C., from about 635° C. to about 665° C., from about 640° C. toabout 665° C., from about 645° C. to about 665° C., or from about 650°C. to about 665° C.). In one or more specific embodiments, heating thestack comprises heating the stack to the first sag temperature or to thesecond sag temperature.

In one or more embodiments of the method, the first sag depth and/or thesecond sag depth is in a range from about 6 mm to about 25 mm. Forexample, one or both the first sag depth and the second sag depth may bein a range from about 2 mm to about 25 mm, from about 4 mm to about 25mm, from about 5 mm to about 25 mm, from about 6 mm to about 25 mm, fromabout 8 mm to about 25 mm, from about 10 mm to about 25 mm, from about12 mm to about 25 mm, from about 14 mm to about 25 mm, from about 15 mmto about 25 mm, from about 2 mm to about 24 mm, from about 2 mm to about22 mm, from about 2 mm to about 20 mm, from about 2 mm to about 18 mm,from about 2 mm to about 16 mm, from about 2 mm to about 15 mm, fromabout 2 mm to about 14 mm, from about 2 mm to about 12 mm, from about 2mm to about 10 mm, from about 2 mm to about 8 mm, from about 6 mm toabout 20 mm, from about 8 mm to about 18 mm, from about 10 mm to about15 mm, from about 12 mm to about 22 mm, from about 15 mm to about 25 mm,or from about 18 mm to about 22 mm.

In one or more embodiments, the method includes positioning or placingthe stack on a female mold and heating the stack as it is positioned onthe female mold. In some embodiments, co-shaping the stack includessagging the stack using gravity through an opening in the female mold.As used herein, term such as “sag depth” refer to shaping depth achievedby sagging or other co-shaping process.

In one or more embodiments, the method includes applying a male mold tothe stack. In some embodiments, the male mold is applied while the stackis positioned or placed on a female mold.

In one or more embodiments, the method includes applying a vacuum to thestack to facilitate co-shaping the stack. In some embodiments, thevacuum is applied while the stack is positioned or placed on a femalemold.

In one or more embodiments, the method includes heating the stack at aconstant temperature while varying the duration of heating until theco-shaped stack is formed. As used herein, constant temperature means atemperature that is ±3° C. from a target temperature, ±2° C. from atarget temperature, or ±1° C. from a target temperature.

In one or more embodiments, the method includes heating the stack for aconstant duration, while varying the temperature of heating until theco-shaped stack is formed. As used herein, constant duration means aduration that is ±10 seconds from a target duration, ±7 seconds from atarget duration, ±5 seconds from a target duration, or ±3 seconds from atarget duration.

In one or more embodiments, the method includes co-shaping the stack byheating the stack at a constant temperature (as defined herein) duringco-shaping. In one or more embodiments, the method includes co-shapingthe stack by heating the stack at a constantly increasing temperatureduring co-shaping. As used herein, the term constantly increasing mayinclude a linearly increasing temperature or a temperature thatincreases stepwise in regular or irregular intervals.

In one or more embodiments, the method includes generating a temperaturegradient in the stack between the central portion and the edge portionof the stack. In some instances, generating a temperature gradientcomprises applying heat unevenly to the central portion and the edgeportion. In some embodiments, more heat is applied to the centralportion than is applied to the edge portion. In other embodiments, moreheat is applied to the edge portion than is applied to the centralportion. In some embodiments, generating a temperature gradientcomprises reducing the heat applied to one of the central portion andthe edge portion compared to heat applied to the other of the centralportion and the edge portion. In some instances, generating atemperature gradient comprises reducing the heat applied to the centralportion compared to the heat applied to the edge portion. In someembodiments, generating a temperature includes reducing the heat appliedto the edge portion compared to the heat applied to the central portion.Heat may be reduced to the central portion or edge portion by physicalmeans such as by shielding such portions with a physical barrier orthermal barrier or adding a heat sink to such portions.

In one or more embodiments, the method includes generating an attractiveforce between the first glass substrate and the second glass substrate.The method includes generating the attractive force while heating thestack and/or while co-shaping the stack. In some embodiments, generatingthe attractive force includes generating an electrostatic force.

In one or more embodiments, the method includes generating a vacuumbetween the first glass substrate and the second glass substrate. Themethod includes generating the vacuum while heating the stack and/orwhile co-shaping the stack. In some embodiments, generating the vacuumincludes heating both the stack whereby one of the first glass substrateand the second substrate (whichever is positioned below the other in thestack) begins to curve before the other of the first glass substrate andthe second glass substrate. This curving of one of the first glasssubstrate and the second glass substrate creates a vacuum between thefirst glass substrate and the second glass substrate. This vacuum causesthe glass substrate that does not curve first (i.e., the glass substratethat does not curve while the other glass substrate begins to sag) tobegin to curve with the other glass substrate. In one or moreembodiments, the method includes creating and maintaining contactbetween the respective peripheral portions (315, 325) of the first glasssubstrate and the second substrate to generate and/or maintain thevacuum between the glass substrates. In one or more embodiments, thecontact is maintained along the entire peripheral portions (315, 325).In one or more embodiments, the contact is maintained until the sagdepth is achieved in one or both of the first glass substrate and thesecond glass substrate.

In one or more embodiments, the method includes forming a temporary bondbetween the first glass substrate and the second glass substrate. Insome embodiments, the temporary bond may include an electrostatic forceor may include a vacuum force (which may be characterized as an air filmbetween glass substrates). The method includes forming the temporarybond while heating the stack and/or while co-shaping the stack. As usedherein, the phrase “temporary bond” refers to a bond that can beovercome by hand or using equipment known in the art for separatingco-shaped glass substrates (which do not include an interlayertherebetween).

To evaluate and characterize the mechanism for the temporary bond, thefirst glass substrate and the second glass substrate were stackedtogether, with a layer of separation powder (e.g., CaCO3, talc, etc.)disposed between the first glass substrate and the second glasssubstrate. The viscosity at 630° C. of the second glass substrate isgreater than the viscosity at 630° C. of the first glass substrate, andthe second glass substrate is positioned on top of the first glasssubstrate. To mathematically characterize the formation of a temporarybond, it was assumed that an air film (or gap having a distance) existsbetween the first glass substrate and the second glass substrate that isapproximately equal to the largest diameter of the separation powderparticles (e.g., in a range from about 10 micrometers to about 20micrometers). Pressure (P) in the gap within the assumed air filmbetween two glass substrates is governed by Equation 1 below:

$\begin{matrix}{\frac{\partial h}{\partial t} = {\nabla\left( {\frac{h^{3}}{12\mu}{\nabla P}} \right)}} & \lbrack 1\rbrack\end{matrix}$

where, h is the gap between first glass substrate and the second glasssubstrate as a function of time t and μ is the air viscosity. Thisequation relates pressure to gap opening and is valid as long as thegap, h, is minimized or relatively small compared to the maximumthickness of the glass substrates (e.g., the gap to maximum glasssubstrate thickness ratio is less than about 10% or less than about 5%).If the glass substrates are in an elastic state (before being heated orpre-heated), there is no change in the gap distance between the twoglass substrates. When the glass substrates are heated to formingtemperatures and when the viscosity of bottom glass substrate issufficiently low, the second glass substrate (positioned under the firstglass substrate) will tend to curve away (or sag away, in the case whereco-shaping includes co-sagging) from first glass substrate; however forseparation to occur, air must enter between glass substrates from theedges, which creates lower pressure (vacuum or suction) between the twoglass substrates that will prevent the second glass substrate fromcurving away or separating from the first glass substrate.

Formation of a temporary bond caused by a suction or vacuum forcebetween the glass substrates was verified through simulation. FIG. 9shows a simulation of co-shaping two glass substrates having differingviscosity at 630° C., with air flow effects.

In the simulation, the first glass substrate has a thickness of 2.1 mmand is a soda lime silicate glass substrate that is positionedunderneath the second glass substrate, which has a thickness of 0.55 mmand is an aluminosilicate glass substrate. The aluminosilicate glasssubstrate includes a composition of 67 mol % SiO2, 8.52 mol % Al2O3, 14mol % Na2O, 1.2 mol % K2O, 6.5 mol % MgO, 0.5 mol % CaO, and 0.2 mol %SnO2. The simulation included a steel frame 900 having a thickness of 2mm that supported the first and second glass substrate stack aroundtheir periphery. The frame had a length and width of 298 mm. Both thefirst and second glass substrates had a length and width of 300 mm. Theinitial gap between first and second glass substrates was 25 μm. FIG. 9shows one-quarter (¼) of the complete image of the first and secondglass substrates after the simulation.

FIG. 10 shows the temperature profile that was applied in the simulationunder gravity (as-is), during which the substrates were allowed to sag.FIG. 9 illustrates the resulting co-shaped stack of the first and secondglass substrates at 120 seconds, after the temperature is returned tothe starting temperature of 400° C. The results of simulations show thatthe first and the second glass substrates are separated by a gap ordistance of 0.675 mm at the center point of both glass substrates after129 seconds. A source of separation can be seen in FIG. 9, where theplates have become separated in the corner. This separation is driven bymechanical forces related to bending the glass substrates in the corner.The second glass substrate (positioned on top of the first glasssubstrate) bends to a lesser extent due to its higher viscosity,resulting in an opening in the corner. This opening allows air to enterand reduces the effect of pressure between the glass substrates. FIG. 11shows the reduced pressure magnitude, especially in the corner. In FIG.11, the legend shows pressure approaching atmospheric pressure (max,atmospheric pressure) and a negative pressure (min, greatest pressure).Specifically, FIG. 11 shows the pressure gradient (in units of Pascals)at the end of the high temperature portion of the co-shaping process andshows a difference in pressure at the corner versus the at the centerpoint indicating an opening between plates that allows air to enterbetween the first and second glass substrates.

This observation indicated closing the opening in the corner shouldpromote formation of a temporary bond between the first and second glasssubstrates. This was observation and the solution of closing the openingwas confirmed by experimentation (Examples A-D). In Examples A and B, afirst glass substrate was a soda lime silicate glass having a thicknessof 2.1 mm and the second glass substrate was an aluminosilicate glasshaving a thickness of 0.55 mm, which was positioned on top of the firstglass substrate. The first and second glass substrates had length andwidth dimensions of 12 inches (12 inches×12 inches). The aluminosilicateglass substrate includes a composition of 67 mol % SiO2, 8.52 mol %Al2O3, 14 mol % Na2O, 1.2 mol % K2O, 6.5 mol % MgO, 0.5 mol % CaO, and0.2 mol % SnO2. In Example A, no reinforcement was applied to the cornerlocations of the stack and the stack was co-shaped in a static furnace.In Example B, reinforcement was applied, in the form of a metallic clip,to each of the four corners of the stack to clamp together the first andsecond glass substrate at each corner of the stack before co-shaping inthe same static furnace. Table 1 compares the mismatch in sag depths forExamples A and B. Example B showed a reduced mismatch when reinforcementwas applied, indicating the effectiveness of closing the opening createdat the corners of the stack during bending. As used herein, mismatchindicates a difference in sag depth between the first and second glasssubstrate. For example, if first glass substrate achieves a sag depth of10 mm, and the second glass substrate achieves a sag depth of 5 mm,there is a shape mismatch of 5 mm.

TABLE 1 Shape mismatch between first glass substrate and second glasssubstrate after co-sagging with and without clips attached at the cornerlocation of the stack. Second glass substrate thickness First glasssubstrate (aluminosilicate, top thickness (SLG, Shape Example position)bottom position) Clip mismatch A 0.55 mm 2.1 mm No 3.3 mm (baseline) B0.55 mm 2.1 mm Yes 1.7 mm

As illustrated in Table 1, in one or more embodiments, the method mayinclude forming a temporary bond between the first and second glasssubstrates by preventing or closing any openings between the glasssubstrates at a portion of the edge or periphery (e.g., the corners) ofthe stack or the entire edge or periphery of the stack. In one or moreembodiments, the method may include forming and/or maintaining atemporary bond between the first and second glass substrates bymaintaining contact (direct or indirect via a separation powder orintervening material) between the glass substrates at a portion of theedge or periphery (e.g., the corners) of the stack or the entire edge orperiphery of the stack.

Alternative methods of forming the temporary bond were evaluated inExamples C and D. In Examples C and D, a first glass substrate was asoda lime silicate glass having a thickness of 2.1 mm and the secondglass substrate was an aluminosilicate glass having a thickness of 0.7mm, which was positioned on top of the first glass substrate. The firstand second glass substrates had length and width dimensions of 12 inches(12 inches×12 inches). The aluminosilicate glass substrate includes acomposition of 67 mol % SiO2, 8.52 mol % Al2O3, 14 mol % Na2O, 1.2 mol %K2O, 6.5 mol % MgO, 0.5 mol % CaO, and 0.2 mol % SnO2. In Example C, noreinforcement was applied to the stack before it was co-shaped in astatic furnace. In Example D, a mechanical means of closing the openingwas used and included placing counterweights on the stack at or near thecorners before co-shaping in the same static furnace. Table 2 comparesthe measured shape mismatch between Example C and D. Again, a lowermismatch is achieved when using counterweights to form or maintain thetemporary bond between the first and second glass substrates.

TABLE 2 Shape mismatch between first glass substrate and second glasssubstrate after co-sagging with and without counterweights placed on topof the stack at the corner locations. Second glass First glass substratesubstrate thickness thickness (SLG, (aluminosilicate, bottom Counter-Shape Example top position) position) weight mismatch C 0.7 mm 2.1 mm No1.8 mm (baseline) D 0.7 mm 2.1 mm Yes 0.9 mm

Numerical analysis was also performed to simulate the effect of atemporary bond and the resulting substrate separation. FIG. 12 shows animage of an exemplary reinforcement (in the form of a clip) applied atthe corner in a numerical simulation. The particular design shown inFIG. 12 exerts a force of 0.4 N on the stack over a length of about 6mm. As a result, the maximum separation between glass substrates withreinforcement on the corners is reduced to 0.164 mm at 129 seconds, asshown in FIG. 13 (compared to a 0.675 mm gap that was seen in FIG. 9when no clips were used). The use of additional reinforcement along theedges of the substrates farther away from the corners would furtherreduce separation. In addition, the use of glass compositions that haveviscosities that are more closely matched than the soda lime silicateand aluminosilicate glasses used in the simulations would produce evenless separation between the glass substrates. FIG. 13 shows thesimulated change in pressure magnitude across the area of the stack ofFIG. 12, indicating the formation of a temporary bond via a vacuumforce.

The method of forming a temporary bond was applied to glass substrateshaving a size and shape for use in an automotive windshield. In ExamplesE and F, a first glass substrate was a soda lime silicate glass having athickness of 2.1 mm and the second glass substrate was analuminosilicate glass having a thickness of 0.7 mm, which was positionedon top of the first glass substrate. Example E included two runs duringwhich no reinforcement was applied to the stack before the stack wasplaced on a bending tool and co-shaped by co-sagging in a lehr furnace.Example F included two runs during which clips were applied around theperiphery of the stack including at or near the corners beforeco-shaping in the same manner as Example E.

FIGS. 14A-B and 15A-B show the shape mismatch between the first glasssubstrate and the second glass substrates for each run of Examples E andF, respectively. Example E demonstrated a shape mismatch in a range fromabout 6.2 mm (FIG. 14A) and 5.5 mm (FIG. 14B). Example F demonstrated a0.1 mm shape mismatch in both runs (FIGS. 15A-B). Specifically, thefirst glass substrate achieved a 12.1 mm sag depth and the second glasssubstrate achieved a 12 mm sag depth in both runs.

Examples G and H used the same first and second glass substrates asExamples E and F and the same co-shaping process and equipment, but usedcounterweights instead of clips for reinforcement. Example G includedthree runs without reinforcement, and each run resulted in a shapemismatch of about 10 mm, as show in FIGS. 16A-C. Example H includedthree runs with each run including counterweights positioned at or nearthe corners of the stack. As shown in FIGS. 17A-C, counterweights at thecorner locations resulted in a shape mismatch of less than 0.5 mm.

As shown above, numerical models and experimental data show the effectof pressure distribution and resulting air flow from the corners of astack on the shape mismatch between glass substrates. Models predictedthat a lack of a temporary bond between the glass substrate duringco-shaping will result in a large shape mismatch between glasssubstrates due to viscosity and bending stiffness difference betweenglass substrate. Experiments confirmed simulation observations thatclosing or preventing air passage between glass substrates will resultin a much improved shape match. The negative pressure (or vacuum force)generated between glass substrate during co-shaping keeps the two glasssubstrates (with different viscosities) together. As long as a seal canbe maintained at the glass substrate edges a good shape match can beachieved between two glass substrates having different viscosities.

In one or more embodiments, the method includes preventing wrinkling atthe peripheral portions (315, 325) of the first glass substrate and thesecond glass substrate. In one or more embodiments, preventing wrinklingincludes shielding at least a portion or the entire peripheral portions(315, 325) of the first and second glass substrates from the heat thestack during bending.

In one or more embodiments, the method may include placing separationpowder between the first glass sheet and the second glass sheet beforeheating and co-shaping.

In some embodiments, the method includes inserting an interlayer betweenthe first curved glass substrate and the second curved glass substrate,and laminating the first curved glass substrate, the interlayer, and thesecond curved glass substrate together.

EXAMPLES

Various embodiments will be further clarified by the following examples.

Example 1

Three glass substrates were considered for use in a shaped laminate.Substrate A was made from a soda lime glass composition. Substrate B1 isa three-layer glass composite including a core layer made from a firstcomposition and two clad layers surrounding the core layer made from asecond composition having a different coefficient of thermal expansion,causing glass substrates made from composition B1 to be mechanicallystrengthened. Substrate B2 is made from an aluminosilicate glasscomposition (including about 67 mol % SiO2, 8.52 mol % Al2O3, 14 mol %Na2O, 1.2 mol % K2O, 6.5 mol % MgO, 0.5 mol % CaO, and 0.2 mol % SnO2)that was capable of being chemically strengthened after the bendingprocess is complete. The respective viscosity as a function oftemperature for each of Substrate A, Substrate B1 and Substrate B2 isshown in FIG. 4.

A sample of Substrate A having a thickness of 2 mm was saggedindividually by heating in a lehr furnace to a maximum temperature of630° C. for 110 seconds (including indexing time to move from onestation in the lehr to another) and achieved a sag depth of about 20 mm.Substrates B1 and B2 were individually subjected to the same saggingconditions as Substrate A to investigate whether glass substrates madefrom different glass compositions could be co-shaped (and contrary tothe general understanding the in the field).

In a first approximation, the temperature of the glass substrates wasassumed to be the same as the set point of the lehr furnace (i.e., thetarget temperature entered into the lehr furnace) and the respectiveviscosity of the glass substrates at 630° C. and 660° C. wasapproximated as shown in Table 3.

TABLE 3 Viscosity information for Substrates A, B1 and B2. Substrate ASubstrate B1 Substrate B2 viscosity viscosity viscosity Temperature(poises) (poises) (poises) 630° C. 6 × 10⁹ 1.8.10¹¹ 4.5.10¹² 660° C. 8 ×10⁸ 3 × 10¹⁰

Substrate B1 had a thickness of 0.55 mm and was sagged individually byheating in a lehr furnace to a maximum temperature of 630° C. for 110seconds (including indexing time to move from one station in the lehr toanother) and achieved a sag depth of about 2 ram. This result isexpected in view of the higher viscosity exhibited by composition B1 (incomparison with composition A).

Substrate B1 was stacked on top of Substrate A, and this stack was thenco-sagged by heating in a lehr furnace to a maximum temperature of 630°C. for 110 seconds (including indexing time to move from one station inthe lehr to another). Based on the known understanding of glassviscosity, it was expected that each of Substrate A and Substrate B1(while in the stack) would achieve substantially the same sag depth asachieved when the substrates were individually sagged. Surprisingly, thestack (including both Substrate A and Substrate B1) achieved a sag depthof about 6 mm.

A stack with Substrate B1 on stacked on top of Substrate A was thenco-sagged by heating in a lehr furnace to a maximum temperature of 660°C. for 110 seconds (including indexing time to move from one station inthe lehr to another). The sagging of both Substrate A and Substrate B1(while in the stack) was the substantially identical and their sag depthincreased to 20 mm.

Without being bound by theory, it is believed that a temporary bond isformed between the two glass substrates during the co-sagging process,which prevents the glass substrate made from composition A from saggingtoo deep and which facilitates sagging of the glass substrate made fromcomposition B 1.

Without being bound by theory it is also believed that the stackapproximately exhibits an effective viscosity based on the individualglass substrate thicknesses and viscosities at a given temperature,based on Equation (1). Accordingly, Substrate A sagged individually to asag depth of 20 mm after being heated to 630° C. at which the viscosityof Substrate A is 6×10⁹ poises. However, when a stack includingSubstrate B1 stacked on top of Substrate A was heated to 660° at whichthe effective viscosity according to Equation (1) is 6.86×10⁹ poises(which approaches the viscosity of Substrate A at 630° C.), the stackachieved a sag depth of 20 mm. Table 4 below shows the viscosity ofSubstrate A and the effective viscosity of the stack including SubstrateA and Substrate B1. It is believed that the small difference between theeffective viscosity of the stack at 660° C. and the viscosity ofSubstrate A at 630° C. is due to possible differences between the glasstemperature and the lehr furnace set point. In addition, it is believedthe difference in effective viscosity is due to the mass differencebetween the stacks. Heat is applied for the same duration to bothstacks; however, the difference in effective viscosity is due toadditional thickness of glass (i.e., having at thickness of 0.7 mm) toheat for shaping.

Accordingly, even glass substrates having very different viscositiesfrom one another can be successfully co-sagged according to theembodiments described herein.

TABLE 4 Viscosities of Substrate A, Substrate B1, and the effectiveviscosity of a stack including Substrate A and Substrate B. Substrate ASubstrate B1 Effective viscosity viscosity viscosity of SubstratesTemperature (poises) (poises) A + B1 (poises) 630° C. 6 × 10⁹ 660° C. 8× 10⁸ 3 × 10¹⁰ 6.86 × 10⁹

Substrate A was placed on top of Substrate B1 to form a stack. The stackwas then heated to a temperature of about 660° C. and achieved a sagdepth exceeding 20 mm. Without being bound by theory, it is theorizedthat Substrate B1 retained Substrate A from sagging further, despite theadditional weight of thicker Substrate A on thinner Substrate B1.Moreover, the increased sag depth of the stack compared to Substrate B1alone is believed to be due to temporary bond formed between thesubstrates during co-sagging. Without being bound by theory, suchtemporary bonding may include the formation of an attractive forcebetween the substrates (which may include an electrostatic force).

Substrate B2 was placed on top of Substrate A to form a stack. As shownin FIG. 4, there is a greater difference in the viscosity curves ofSubstrate A and Substrate B2 (in comparison to the curves of Substrate Aand Substrate B1). When Substrate B2 had a thickness of 0.7 mm, thestack did not achieve a suitable sag depth; however, when Substrate B2had a thickness of 0.55 mm, the stack achieved a suitable sag depth.Without being bound by theory, it is believed that a thinner glasssubstrate stacked on a thicker glass substrate creates improved contactand potentially improved temporary bonding between the two glasssubstrates, which is believed to result in improved co-shaping.

Example 1 shows that a pair of glass substrates having differentthickness and different viscosity (and likely composition) can besuccessfully co-shaped and such co-shaping is driven by an effectiveviscosity of the stack.

Example 2

Comparative Examples 2A-2B, Examples 2C-2F, Comparative Example 2G, andExamples 2H-2N were formed in a lehr furnace. Comparative Examples 2A-2Band 2G are single glass substrates, and Examples 2C-2F and 2H-2N areco-shaped laminates according to one or more embodiments. Table 5 showsthe construction of each example, and the achieved sag depth. In theexamples, the top glass substrate is placed on the bottom glasssubstrate to form a stack. Where only a single glass substrate is used,it is denoted as the bottom glass substrate. The sag depth of each glasssubstrate is measured after separating the glass substrates, whereapplicable.

TABLE 5 Example 2 configurations and sag depths. Sag Bottom Top depth ofSag glass glass bottom depth of Lehr substrate substrate glass top glassSet and and substrate substrate point Example thickness thickness (mm)(mm) (° C.) 2A Substrate A — 19.23 — 630 (2.1 mm) 2B Substrate B1 — 2.01— 630 (0.55 mm) 2C Substrate A Substrate B1 6.26 6.02 630 (2.1 mm) (0.55mm) 2D Substrate B1 Substrate A 6.07 5.45 630 (0.55 mm) (2.1 mm) 2ESubstrate A Substrate B1 5.01 5.06 630 (2.1 mm) (0.55 mm) 2F Substrate ASubstrate B2 8.08 0 630 (2.1 mm) (0.7 mm) 2G Substrate A — 20.07 — 630(2.1 mm) 2H Substrate B1 — 1.46 — 630 (0.55 mm) 2I Substrate A SubstrateB2 0.56 0.31 630 (2.1 mm) (0.55 mm) 2J Substrate A Substrate A 17.0216.85 630 (2.1 mm) (0.7 mm) 2K Substrate A Substrate B1 19.22 20.07 660(2.1 mm) (0.55 mm) 2L Substrate A Substrate B2 1.29 0.29 630 (2.1 mm)(0.55 mm) 2M Substrate A Substrate B1 17.28 17.39 655 (2.1 mm) (0.55 mm)2N Substrate A Substrate B1 26.72 25.94 665 (2.1 mm) (0.55 mm)

Aspect (1) of this disclosure pertains to a laminate comprising: a firstcurved glass substrate comprising a first major surface, a second majorsurface opposing the first major surface, a first thickness defined asthe distance between the first major surface and second major surface,and a first sag depth of about 2 mm or greater, the first curved glasssubstrate comprising a first viscosity (poises) at a temperature of 630°C.; a second curved glass substrate comprising a third major surface, afourth major surface opposing the third major surface, a secondthickness defined as the distance between the third major surface andthe fourth major surface, and a second sag depth of about 2 mm orgreater, the second curved glass substrate comprising a second viscositythat is greater than the first viscosity at a temperature of 630° C.;and an interlayer disposed between the first curved glass substrate andthe second curved glass substrate and adjacent the second major surfaceand third major surface, wherein the first sag depth is within 10% ofthe second sag depth and a shape deviation between the first glasssubstrate and the second glass substrate of ±5 mm or less as measured byan optical three-dimensional scanner, and wherein one of or both thefirst major surface and the fourth major surface exhibit an opticaldistortion of less than 200 millidiopters as measured by an opticaldistortion detector using transmission optics according to ASTM 1561,and wherein the first major surface or the second major surfacecomprises a membrane tensile stress of less than 7 MPa as measured by asurface stressmeter, according to ASTM C1279.

Aspect (2) of this disclosure pertains to the laminate of Aspect (1),wherein, at a temperature of about 630° C., the second viscosity is in arange from about 10 times the first viscosity to about 750 times thefirst viscosity.

Aspect (3) of this disclosure pertains to the laminate of Aspect (1) orAspect (2), wherein the glass stack comprises an effective viscositythat is between the first viscosity and the second viscosity at atemperature (T) in a range from about 500° C. to about 700° C., and isdetermined by the equation:μ_(eff)(T)=((μ₁(T)t₁)/(t₁+t₂))+((μ₂(T)t₂)/(t₁+t₂)), where μ₁(T) is theviscosity of the first curved glass substrate at temperature (T), t₁ isthe thickness of the first curved glass substrate, μ₂(T) is theviscosity of the second curved glass substrate at temperature (T), t₂ isthe thickness of the second curved glass substrate.

Aspect (4) of this disclosure pertains to the laminate of any one ofAspects (1) through (3), wherein the second thickness is less than thefirst thickness.

Aspect (5) of this disclosure pertains to the laminate of any one ofAspects (1) through (4), wherein the first thickness is from about 1.6mm to about 3 mm, and the second thickness is in a range from about 0.1mm to less than about 1.6 mm.

Aspect (6) of this disclosure pertains to the laminate of any one ofAspects (1) through (5), wherein first curved substrate comprises afirst sag temperature and the second curved glass substrate comprises asecond sag temperature that differs from the first sag temperature.

Aspect (7) of this disclosure pertains to the laminate of Aspect (6),wherein the difference between the first sag temperature and the secondsag temperature is in a range from about 30° C. to about 150° C.

Aspect (8) of this disclosure pertains to the laminate of any one ofAspects (1) through (7), wherein the shape deviation is about ±1 mm orless.

Aspect (9) of this disclosure pertains to the laminate of any one ofAspects (1) through (8), wherein the shape deviation is about ±0.5 mm orless.

Aspect (10) of this disclosure pertains to the laminate of any one ofAspects (1) through (9), wherein the optical distortion is about 100millidiopters or less.

Aspect (11) of this disclosure pertains to the laminate of any one ofAspects (1) through (10), wherein the membrane tensile stress is about 5MPa or less.

Aspect (12) of this disclosure pertains to the laminate of any one ofAspects (1) through (11), wherein the second sag depth is in a rangefrom about 5 mm to about 30 mm.

Aspect (13) of this disclosure pertains to the laminate of any one ofAspects (1) through (12), wherein the first major surface or the secondmajor surface comprises a surface compressive stress of less than 3 MPaas measured by a surface stress meter.

Aspect (14) of this disclosure pertains to the laminate of any one ofAspects (1) through (13), wherein the laminate is substantially free ofvisual distortion as measured by ASTM C1652/C1652M.

Aspect (15) of this disclosure pertains to the laminate of any one ofAspects (1) through (14), wherein the second curved glass substrate isstrengthened.

Aspect (16) of this disclosure pertains to the laminate of Aspect (15),wherein the second curved glass substrate is chemically strengthened,mechanically strengthened or thermally strengthened.

Aspect (17) of this disclosure pertains to the laminate of Aspect (15)or Aspect (16), wherein the first glass curved substrate isunstrengthened.

Aspect (18) of this disclosure pertains to the laminate of Aspect (15)or Aspect (16), wherein the first curved glass substrate isstrengthened.

Aspect (19) of this disclosure pertains to the laminate of any one ofAspects (1) through (18), wherein the first curved glass substratecomprises a soda lime silicate glass.

Aspect (20) of this disclosure pertains to the laminate of any one ofAspects (1) through (19), wherein the first curved glass substratecomprises an alkali aluminosilicate glass, alkali containingborosilicate glass, alkali aluminophosphosilicate glass, or alkalialuminoborosilicate glass.

Aspect (21) of this disclosure pertains to the laminate of any one ofAspects (1) through (20), wherein the first curved glass substratecomprises a first length and a first width, either one of or both thefirst length and the first width is about 0.25 meters or greater.

Aspect (22) of this disclosure pertains to the laminate of any one ofAspects (1) through (21), wherein the first curved glass substratecomprises a first length, and a first width, and the second curved glasssubstrate comprises a second length that is within 5% of the firstlength, and a second width that is within 5% of the first width.

Aspect (23) of this disclosure pertains to the laminate of any one ofAspects (1) through (22), where the laminate is complexly curved.

Aspect (24) of this disclosure pertains to the laminate of any one ofAspects (1) through (23), wherein the laminate comprises automotiveglazing or architectural glazing.

Aspect (25) of this disclosure pertains to a vehicle comprising: a bodydefining an interior and an opening in communication with the interior;a complexly curved laminate disposed in the opening, the laminatecomprising a first curved glass substrate comprising a first majorsurface, a second major surface opposing the first major surface, afirst thickness defined as the distance between the first major surfaceand second major surface, and a first sag depth of about 2 mm orgreater, the first curved glass substrate comprising a first viscosity(poises), a second curved glass substrate comprising a third majorsurface, a fourth major surface opposing the third major surface, asecond thickness defined as the distance between the third major surfaceand the fourth major surface, and a second sag depth of about 2 mm orgreater, the second curved glass substrate comprising a second viscositythat greater than the first viscosity at a temperature of about 630° C.,and an interlayer disposed between the first curved glass substrate andthe second curved glass substrate and adjacent the second major surfaceand third major surface, wherein the first sag depth is within 10% ofthe second sag depth and a shape deviation between the first glasssubstrate and the second glass substrate of ±5 mm or less as measured byan optical three-dimensional scanner, and wherein one of or both thefirst major surface and the fourth major surface exhibit an opticaldistortion of less than 200 millidiopters as measured by an opticaldistortion detector using transmission optics according to ASTM 1561,and wherein the first major surface or the second major surfacecomprises a membrane tensile stress of less than 7 MPa as measured by asurface stressmeter, according to ASTM C1279.

Aspect (26) of this disclosure pertains to the vehicle of Aspect (25),wherein, at a temperature of 630° C., the second viscosity is in a rangefrom about 10 times the first viscosity to about 750 times the firstviscosity.

Aspect (27) of this disclosure pertains to the laminate of Aspect (25)or Aspect (26) wherein the second thickness is less than the firstthickness.

Aspect (28) of this disclosure pertains to the laminate of any one ofAspects (25) through (27), wherein the second thickness is less thanabout 1.6 mm.

Aspect (29) of this disclosure pertains to the laminate of any one ofAspects (25) through (28), wherein the first thickness is from about 1.6mm to about 3 mm, and the second thickness is in a range from about 0.1mm to less than about 1.6 mm.

Aspect (30) of this disclosure pertains to the laminate of any one ofAspects (25) through (29), wherein first curved substrate comprises afirst sag temperature and the second curved glass substrate comprises asecond sag temperature that differs from the first sag temperature.

Aspect (31) of this disclosure pertains to the laminate of any one ofAspects (25) through (30), wherein the shape deviation is about ±1 mm orless.

Aspect (32) of this disclosure pertains to the laminate of any one ofAspects (25) through (31), wherein the optical distortion is about 100millidiopters or less.

Aspect (33) of this disclosure pertains to the laminate of any one ofAspects (25) through (32), wherein the membrane tensile stress is about5 MPa or less.

Aspect (34) of this disclosure pertains to the laminate of any one ofAspects (25) through (33), wherein the second sag depth is in a rangefrom about 5 mm to about 30 mm.

Aspect (35) of this disclosure pertains to the laminate of any one ofAspects (25) through (34), wherein the first major surface or the secondmajor surface comprises a surface compressive stress of less than 3 MPaas measured by a surface stress meter.

Aspect (36) of this disclosure pertains to the laminate of any one ofAspects (25) through (35), wherein the first curved glass substratecomprises a first tint and the second curved glass substrate comprises asecond tint that differs from the first tint in the CIE L*a*b* (CIELAB)color space.

Aspect (37) of this disclosure pertains to the laminate of any one ofAspects (25) through (36), wherein the laminate is substantially free ofvisual distortion as measured by ASTM C1652/C1652M.

Aspect (38) of this disclosure pertains to a method of forming a curvedlaminate comprising: forming a stack comprising a first glass substratecomprising a first viscosity (poises) and a first sag temperature and asecond glass substrate, the second glass substrate comprising a secondviscosity that greater than the first viscosity at a temperature of 630°C. and a second sag temperature that differs from the first sagtemperature; and heating the stack and co-shaping the stack to form aco-shaped stack, the co-shaped stack comprising a first curved glasssubstrate having a first sag depth and a second curved glass substrateeach having a second sag depth, wherein the first sag depth and thesecond sag depth are greater than 2 mm and within 10% of one another.

Aspect (39) of this disclosure pertains to the method of Aspect (38),wherein the second glass substrate is disposed on the first glasssubstrate.

Aspect (40) of this disclosure pertains to the method of Aspect (38),wherein the first glass substrate is disposed on the second glasssubstrate.

Aspect (41) of this disclosure pertains to the method of any one ofAspects (38) through (40), wherein heating the stack comprises heatingthe stack to a temperature different from the first sag temperature andthe second sag temperature.

Aspect (42) of this disclosure pertains to the method of any one ofAspects (38) through (41), wherein heating the stack comprises heatingthe stack to a temperature between the first sag temperature and thesecond sag temperature.

Aspect (43) of this disclosure pertains to the method of any one ofAspects (38) through (40), wherein heating the stack comprises heatingthe stack to the first sag temperature.

Aspect (44) of this disclosure pertains to the method of any one ofAspects (38) through (40), wherein heating the stack comprises heatingthe stack to the second sag temperature.

Aspect (45) of this disclosure pertains to the method of any one ofAspects (38) through (44), wherein the first sag depth or the second sagdepth is in a range from about 6 mm to about 30 mm.

Aspect (46) of this disclosure pertains to the method of any one ofAspects (38) through (45), further comprising placing the stack on afemale mold and heating the stack on the female mold.

Aspect (47) of this disclosure pertains to the method of Aspect (46),wherein co-shaping the stack comprises sagging the stack using gravitythrough an opening in the female mold.

Aspect (48) of this disclosure pertains to the method of Aspect (46) orAspect (47), further comprising applying a male mold to the stack.

Aspect (49) of this disclosure pertains to the method of Aspect (46) orAspect (47), further comprising applying a vacuum to the stack tofacilitate co-shaping the stack.

Aspect (50) of this disclosure pertains to the method of any one ofAspects (38) through (49), wherein heating the stack comprises heatingthe stack at a constant temperature while varying the duration ofheating until the co-shaped stack is formed.

Aspect (51) of this disclosure pertains to the method of any one ofAspects (38) through (49), wherein heating the stack comprises heatingthe stack for a constant duration, while varying the temperature ofheating until the co-shaped stack is formed.

Aspect (52) of this disclosure pertains to the method of any one ofAspects (38) through (51), the method of any one of claims 38-51,wherein co-shaping the stack comprises heating the stack at a constanttemperature during co-shaping.

Aspect (53) of this disclosure pertains to the method of any one ofAspects (38) through (51), wherein co-shaping the stack comprisesheating the stack at a constantly increasing temperature duringco-shaping.

Aspect (54) of this disclosure pertains to the method of any one ofAspects (38) through (45), wherein the stack comprises opposing majorsurfaces each comprising a central portion and an edge portionsurrounding the central portion, wherein heating the stack comprisescreating a temperature gradient between the central portion and the edgeportion.

Aspect (55) of this disclosure pertains to the method of Aspect (54),wherein creating a temperature gradient comprises applying heat unevenlyto the central portion and the edge portion.

Aspect (56) of this disclosure pertains to the method of any one ofAspects (38) through (55), further comprising generating anelectrostatic force or a vacuum between the first glass substrate andthe second glass substrate.

Aspect (57) of this disclosure pertains to the method of Aspect (56),wherein the electrostatic force or the vacuum is generated while heatingthe stack to the first sag temperature.

Aspect (58) of this disclosure pertains to the method of Aspect (56),wherein the electrostatic force or the vacuum is generated whileco-shaping the stack.

Aspect (59) of this disclosure pertains to the method of Aspect (56),wherein the electrostatic force or the vacuum is generated while heatingthe stack and co-shaping the stack.

Aspect (60) of this disclosure pertains to the method of any one ofAspects (38) through (59), further comprising forming a temporary bondbetween the first glass substrate and the second glass substrate.

Aspect (61) of this disclosure pertains to the method of Aspect (60),wherein the temporary bond comprises an electrostatic force.

Aspect (62) of this disclosure pertains to the method of any one ofAspects (38) through (61), further comprising placing separation powderbetween the first glass sheet and the second glass sheet before heatingand shaping.

Aspect (63) of this disclosure pertains to the method of any one ofAspects (38) through (61), further comprising inserting an interlayerbetween the first curved glass substrate and the second curved glasssubstrate, and laminating the first curved glass substrate, theinterlayer, and the second curved glass substrate together.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention.

What is claimed is:
 1. A laminate comprising: a first curved glasssubstrate comprising a first major surface, a second major surfaceopposing the first major surface, a first thickness t1 defined betweenthe first major surface and the second major surface, and the firstcurved glass substrate comprising a first viscosity; a second curvedglass substrate comprising a third major surface, a fourth major surfaceopposing the third major surface, a second thickness t2 defined betweenthe third major surface and the fourth major surface, and the secondcurved glass substrate comprising a second viscosity greater than thefirst viscosity at a temperature of 630° C.; an interlayer disposedbetween the first curved glass substrate and the second curved glasssubstrate and adjacent the second major surface and the third majorsurface; and wherein the laminate comprises an effective viscositybetween the first viscosity and the second viscosity at a temperature(T) in a range from about 500° C. to about 700° C., the effectiveviscosity determined by the equation:μeff(T)=(T)μ1)/(t1+t2))+((μ2(T)t2)/(t1+t2)), where μ1(T) is theviscosity of the first curved glass substrate at temperature (T) andμ2(T) is the viscosity of the second curved glass substrate attemperature (T).
 2. The laminate of claim 1, wherein the second curvedglass substrate is a strengthened glass substrate.
 3. The laminate ofclaim 2, wherein the second curved glass substrate is a chemicallystrengthened glass substrate.
 4. The laminate of claim 2, wherein thefirst curved glass substrate is an unstrengthened glass substrate. 5.The laminate of claim 1, wherein t2 is less than t1.
 6. The laminate ofclaim 1, wherein t2 is less than about 1.6 mm.
 7. The laminate of claim1, wherein the first viscosity is in a range from about 1×10⁹ poise toabout 1×10¹⁰ poise at a temperature of 630° C.
 8. The laminate of claim1, wherein the second viscosity is in a range from about 2×10¹⁰ poise toabout 1×10¹³ poise at a temperature of 630° C.
 9. The laminate of claim1, wherein the first curved glass substrate comprises a first sagtemperature in a range from 600° C. to 650° C.
 10. The laminate of claim9, wherein the second curved glass substrate comprises a second sagtemperature greater than 650° C.
 11. The laminate of claim 1, whereinthe first curved glass substrate comprises a first sag temperature, thesecond curved glass substrate comprises a second sag temperature, and adifference between the first sag temperature and the second sagtemperature is about 5° C. or greater.
 12. The laminate of claim 11,wherein the difference in sag temperature is in a range from about 5° C.to about 150° C.
 13. The laminate of claim 1, wherein the secondviscosity is greater than about 2 times the first viscosity at atemperature of 630° C.
 14. A laminate comprising: a first curved glasssubstrate comprising a first major surface, a second major surfaceopposing the first major surface, a first thickness t1 defined betweenthe first major surface and the second major surface, and the firstcurved glass substrate comprising a first viscosity; a second curvedglass substrate comprising a third major surface, a fourth major surfaceopposing the third major surface, a second thickness t2 defined betweenthe third major surface and the fourth major surface less than about 1.6mm, and the second curved glass substrate comprising a second viscositygreater than about 2 times the first viscosity at a temperature of 630°C.; an interlayer disposed between the first curved glass substrate andthe second curved glass substrate and adjacent the second major surfaceand the third major surface; and wherein the laminate comprises aneffective viscosity between the first viscosity and the second viscosityat a temperature (T) in a range from about 500° C. to about 700° C., theeffective viscosity determined by the equation:μeff(T)=(T)t1)/(t1+t2))+((μ2(T)t2)/(t1+t2)), where μ1(T) is theviscosity of the first curved glass substrate at temperature (T) andμ2(T) is the viscosity of the second curved glass substrate attemperature (T).
 15. The laminate of claim 14, wherein the secondviscosity is in a range from about 10 times to about 1000 times greaterthan the first viscosity at 630° C.
 16. The laminate of claim 14,wherein the first viscosity is in a range from about 1×10⁹ poise toabout 1×10¹⁰ poise at a temperature of 630° C.
 17. The laminate of claim16, wherein the second viscosity is in a range from about 2×10¹⁰ poiseto about 1×10¹³ poise at a temperature of 630° C.
 18. The laminate ofclaim 14, wherein the first curved glass substrate comprises a first sagtemperature, the second curved glass substrate comprises a second sagtemperature, and a difference between the first sag temperature and thesecond sag temperature is about 5° C. or greater.
 19. The laminate ofclaim 18, wherein the difference in sag temperature is in a range fromabout 5° C. to about 150° C.
 20. The laminate of claim 14, wherein thesecond curved glass substrate is a strengthened glass substrate.